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 $88.66   10.369%   $97.8532   $97.85   $97.85   $97.90  
  Purchase #2 $203.78   6.814%   $217.6656   $217.67   $217.65   $217.70  
  Purchase #3 $39.90   5.706%   $42.1767   $42.18   $42.20   $42.20  
  Purchase #4 $113.96   4.381%   $118.9526   $118.95   $118.95   $119.00  
  Purchase #5 $47.42   10.321%   $52.3142   $52.31   $52.30   $52.30  
  Purchase #6 $209.46   5.497%   $220.974   $220.97   $220.95   $221.00  
  Purchase #7 $184.42   12.662%   $207.7713   $207.77   $207.75   $207.80  
  7 purchase totals = $887.60       $957.7076   $957.70   $957.65   $957.90