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 $250.57   6.591%   $267.0851   $267.09   $267.10   $267.10  
  Purchase #2 $180.68   13.829%   $205.6662   $205.67   $205.65   $205.70  
  Purchase #3 $74.82   10.801%   $82.9013   $82.90   $82.90   $82.90  
  Purchase #4 $58.52   3.468%   $60.5495   $60.55   $60.55   $60.50  
  Purchase #5 $48.37   11.180%   $53.7778   $53.78   $53.80   $53.80  
  Purchase #6 $65.46   5.569%   $69.1055   $69.11   $69.10   $69.10  
  Purchase #7 $122.27   9.747%   $134.1877   $134.19   $134.20   $134.20  
  7 purchase totals = $800.69       $873.2731   $873.29   $873.30   $873.30