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 $15.29   11.262%   $17.012   $17.01   $17.00   $17.00  
  Purchase #2 $212.88   7.554%   $228.961   $228.96   $228.95   $229.00  
  Purchase #3 $61.29   3.456%   $63.4082   $63.41   $63.40   $63.40  
  Purchase #4 $200.64   7.339%   $215.365   $215.37   $215.35   $215.40  
  Purchase #5 $197.93   5.853%   $209.5148   $209.51   $209.50   $209.50  
  Purchase #6 $159.74   7.648%   $171.9569   $171.96   $171.95   $172.00  
  Purchase #7 $23.81   9.475%   $26.066   $26.07   $26.05   $26.10  
  7 purchase totals = $871.58       $932.2839   $932.29   $932.20   $932.40