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 $245.36   6.692%   $261.7795   $261.78   $261.80   $261.80  
  Purchase #2 $216.67   13.699%   $246.3516   $246.35   $246.35   $246.40  
  Purchase #3 $178.91   8.446%   $194.0207   $194.02   $194.00   $194.00  
  Purchase #4 $226.93   12.731%   $255.8205   $255.82   $255.80   $255.80  
  Purchase #5 $205.65   6.690%   $219.408   $219.41   $219.40   $219.40  
  Purchase #6 $33.86   12.733%   $38.1714   $38.17   $38.15   $38.20  
  Purchase #7 $91.29   6.111%   $96.8687   $96.87   $96.85   $96.90  
  7 purchase totals = $1,198.67       $1,312.4204   $1,312.42   $1,312.35   $1,312.50