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 $111.58   12.804%   $125.8667   $125.87   $125.85   $125.90  
  Purchase #2 $162.36   6.819%   $173.4313   $173.43   $173.45   $173.40  
  Purchase #3 $57.79   7.308%   $62.0133   $62.01   $62.00   $62.00  
  Purchase #4 $242.92   9.767%   $266.646   $266.65   $266.65   $266.60  
  Purchase #5 $120.39   6.764%   $128.5332   $128.53   $128.55   $128.50  
  Purchase #6 $91.65   11.616%   $102.2961   $102.30   $102.30   $102.30  
  Purchase #7 $58.47   5.217%   $61.5204   $61.52   $61.50   $61.50  
  7 purchase totals = $845.16       $920.3070   $920.31   $920.30   $920.20