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 $196.78   13.325%   $223.0009   $223.00   $223.00   $223.00  
  Purchase #2 $10.58   8.317%   $11.4599   $11.46   $11.45   $11.50  
  Purchase #3 $42.35   10.616%   $46.8459   $46.85   $46.85   $46.80  
  Purchase #4 $30.87   5.304%   $32.5073   $32.51   $32.50   $32.50  
  Purchase #5 $232.64   5.507%   $245.4515   $245.45   $245.45   $245.50  
  Purchase #6 $244.56   3.456%   $253.012   $253.01   $253.00   $253.00  
  Purchase #7 $122.50   5.631%   $129.398   $129.40   $129.40   $129.40  
  7 purchase totals = $880.28       $941.6755   $941.68   $941.65   $941.70