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 $202.59   6.764%   $216.2932   $216.29   $216.30   $216.30  
  Purchase #2 $228.86   13.159%   $258.9757   $258.98   $259.00   $259.00  
  Purchase #3 $120.33   7.271%   $129.0792   $129.08   $129.10   $129.10  
  Purchase #4 $171.43   12.528%   $192.9068   $192.91   $192.90   $192.90  
  Purchase #5 $151.85   7.395%   $163.0793   $163.08   $163.10   $163.10  
  Purchase #6 $246.93   6.397%   $262.7261   $262.73   $262.75   $262.70  
  Purchase #7 $41.28   7.395%   $44.3327   $44.33   $44.35   $44.30  
  7 purchase totals = $1,163.27       $1,267.3930   $1,267.40   $1,267.50   $1,267.40