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 $155.62   6.228%   $165.312   $165.31   $165.30   $165.30  
  Purchase #2 $65.49   9.329%   $71.5996   $71.60   $71.60   $71.60  
  Purchase #3 $166.96   6.115%   $177.1696   $177.17   $177.15   $177.20  
  Purchase #4 $237.48   5.747%   $251.128   $251.13   $251.15   $251.10  
  Purchase #5 $216.27   12.197%   $242.6485   $242.65   $242.65   $242.60  
  Purchase #6 $74.51   10.797%   $82.5548   $82.55   $82.55   $82.60  
  Purchase #7 $248.95   9.127%   $271.6717   $271.67   $271.65   $271.70  
  7 purchase totals = $1,165.28       $1,262.0842   $1,262.08   $1,262.05   $1,262.10