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 $56.42   11.229%   $62.7554   $62.76   $62.75   $62.80  
  Purchase #2 $137.56   8.395%   $149.1082   $149.11   $149.10   $149.10  
  Purchase #3 $200.33   5.210%   $210.7672   $210.77   $210.75   $210.80  
  Purchase #4 $62.26   12.360%   $69.9553   $69.96   $69.95   $70.00  
  Purchase #5 $84.96   9.461%   $92.9981   $93.00   $93.00   $93.00  
  Purchase #6 $247.47   3.118%   $255.1861   $255.19   $255.20   $255.20  
  Purchase #7 $210.59   4.137%   $219.3021   $219.30   $219.30   $219.30  
  7 purchase totals = $999.59       $1,060.0724   $1,060.09   $1,060.05   $1,060.20