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 $31.87   5.178%   $33.5202   $33.52   $33.50   $33.50  
  Purchase #2 $242.51   13.413%   $275.0379   $275.04   $275.05   $275.00  
  Purchase #3 $100.37   7.271%   $107.6679   $107.67   $107.65   $107.70  
  Purchase #4 $119.68   12.357%   $134.4689   $134.47   $134.45   $134.50  
  Purchase #5 $244.69   7.125%   $262.1242   $262.12   $262.10   $262.10  
  Purchase #6 $81.84   11.492%   $91.2451   $91.25   $91.25   $91.20  
  Purchase #7 $244.61   11.760%   $273.3761   $273.38   $273.40   $273.40  
  7 purchase totals = $1,065.57       $1,177.4403   $1,177.45   $1,177.40   $1,177.40