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 $92.30   10.485%   $101.9777   $101.98   $102.00   $102.00  
  Purchase #2 $37.64   10.550%   $41.611   $41.61   $41.60   $41.60  
  Purchase #3 $107.83   4.517%   $112.7007   $112.70   $112.70   $112.70  
  Purchase #4 $238.41   11.171%   $265.0428   $265.04   $265.05   $265.00  
  Purchase #5 $223.76   9.494%   $245.0038   $245.00   $245.00   $245.00  
  Purchase #6 $149.35   11.590%   $166.6597   $166.66   $166.65   $166.70  
  Purchase #7 $59.74   9.766%   $65.5742   $65.57   $65.55   $65.60  
  7 purchase totals = $909.03       $998.5699   $998.56   $998.55   $998.60