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 $200.33   12.217%   $224.8043   $224.80   $224.80   $224.80  
  Purchase #2 $13.64   5.335%   $14.3677   $14.37   $14.35   $14.40  
  Purchase #3 $181.63   6.622%   $193.6575   $193.66   $193.65   $193.70  
  Purchase #4 $163.97   11.568%   $182.938   $182.94   $182.95   $182.90  
  Purchase #5 $220.68   11.450%   $245.9479   $245.95   $245.95   $245.90  
  Purchase #6 $21.71   3.464%   $22.462   $22.46   $22.45   $22.50  
  Purchase #7 $169.89   5.562%   $179.3393   $179.34   $179.35   $179.30  
  7 purchase totals = $971.85       $1,063.5167   $1,063.52   $1,063.50   $1,063.50