Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.97   12.856%   $234.7066   $234.71   $234.70   $234.70  
  Purchase #2 $153.68   10.433%   $169.7134   $169.71   $169.70   $169.70  
  Purchase #3 $241.69   7.194%   $259.0772   $259.08   $259.10   $259.10  
  Purchase #4 $126.85   3.550%   $131.3532   $131.35   $131.35   $131.40  
  Purchase #5 $154.94   11.767%   $173.1718   $173.17   $173.15   $173.20  
  Purchase #6 $202.79   7.174%   $217.3382   $217.34   $217.35   $217.30  
  Purchase #7 $167.27   6.108%   $177.4869   $177.49   $177.50   $177.50  
  7 purchase totals = $1,255.19       $1,362.8473   $1,362.85   $1,362.85   $1,362.90