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 $58.92   11.306%   $65.5815   $65.58   $65.60   $65.60  
  Purchase #2 $126.99   6.186%   $134.8456   $134.85   $134.85   $134.80  
  Purchase #3 $209.97   5.543%   $221.6086   $221.61   $221.60   $221.60  
  Purchase #4 $112.43   13.490%   $127.5968   $127.60   $127.60   $127.60  
  Purchase #5 $97.36   13.206%   $110.2174   $110.22   $110.20   $110.20  
  Purchase #6 $187.44   12.232%   $210.3677   $210.37   $210.35   $210.40  
  Purchase #7 $53.90   4.425%   $56.2851   $56.29   $56.30   $56.30  
  7 purchase totals = $847.01       $926.5027   $926.52   $926.50   $926.50