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 $56.37   11.818%   $63.0318   $63.03   $63.05   $63.00  
  Purchase #2 $217.25   13.562%   $246.7134   $246.71   $246.70   $246.70  
  Purchase #3 $201.45   4.833%   $211.1861   $211.19   $211.20   $211.20  
  Purchase #4 $156.28   7.254%   $167.6166   $167.62   $167.60   $167.60  
  Purchase #5 $71.30   10.568%   $78.835   $78.84   $78.85   $78.80  
  Purchase #6 $197.53   10.785%   $218.8336   $218.83   $218.85   $218.80  
  Purchase #7 $230.98   4.733%   $241.9123   $241.91   $241.90   $241.90  
  7 purchase totals = $1,131.16       $1,228.1288   $1,228.13   $1,228.15   $1,228.00