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 $217.48   12.253%   $244.1278   $244.13   $244.15   $244.10  
  Purchase #2 $209.82   10.494%   $231.8385   $231.84   $231.85   $231.80  
  Purchase #3 $26.94   9.583%   $29.5217   $29.52   $29.50   $29.50  
  Purchase #4 $33.38   7.695%   $35.9486   $35.95   $35.95   $35.90  
  Purchase #5 $226.41   10.714%   $250.6676   $250.67   $250.65   $250.70  
  Purchase #6 $200.34   8.167%   $216.7018   $216.70   $216.70   $216.70  
  Purchase #7 $43.92   7.320%   $47.1349   $47.13   $47.15   $47.10  
  7 purchase totals = $958.29       $1,055.9409   $1,055.94   $1,055.95   $1,055.80