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 $59.53   12.517%   $66.9814   $66.98   $67.00   $67.00  
  Purchase #2 $203.32   13.303%   $230.3677   $230.37   $230.35   $230.40  
  Purchase #3 $108.46   11.264%   $120.6769   $120.68   $120.70   $120.70  
  Purchase #4 $164.67   11.353%   $183.365   $183.37   $183.35   $183.40  
  Purchase #5 $31.66   6.810%   $33.816   $33.82   $33.80   $33.80  
  Purchase #6 $122.39   8.250%   $132.4872   $132.49   $132.50   $132.50  
  Purchase #7 $236.30   5.740%   $249.8636   $249.86   $249.85   $249.90  
  7 purchase totals = $926.33       $1,017.5578   $1,017.57   $1,017.55   $1,017.70