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 $76.92   10.466%   $84.9704   $84.97   $84.95   $85.00  
  Purchase #2 $176.78   8.228%   $191.3255   $191.33   $191.35   $191.30  
  Purchase #3 $219.54   11.496%   $244.7783   $244.78   $244.80   $244.80  
  Purchase #4 $97.42   13.490%   $110.562   $110.56   $110.55   $110.60  
  Purchase #5 $50.53   4.716%   $52.913   $52.91   $52.90   $52.90  
  Purchase #6 $229.52   6.365%   $244.1289   $244.13   $244.15   $244.10  
  Purchase #7 $177.42   13.489%   $201.3522   $201.35   $201.35   $201.40  
  7 purchase totals = $1,028.13       $1,130.0303   $1,130.03   $1,130.05   $1,130.10