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 $54.91   12.799%   $61.9379   $61.94   $61.95   $61.90  
  Purchase #2 $175.94   13.536%   $199.7552   $199.76   $199.75   $199.80  
  Purchase #3 $178.56   8.605%   $193.9251   $193.93   $193.95   $193.90  
  Purchase #4 $41.57   9.477%   $45.5096   $45.51   $45.50   $45.50  
  Purchase #5 $143.28   8.276%   $155.1379   $155.14   $155.15   $155.10  
  Purchase #6 $151.84   4.744%   $159.0433   $159.04   $159.05   $159.00  
  Purchase #7 $199.57   7.830%   $215.1963   $215.20   $215.20   $215.20  
  7 purchase totals = $945.67       $1,030.5053   $1,030.52   $1,030.55   $1,030.40