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 $31.93   4.392%   $33.3324   $33.33   $33.35   $33.30  
  Purchase #2 $211.46   9.701%   $231.9737   $231.97   $231.95   $232.00  
  Purchase #3 $91.39   5.872%   $96.7564   $96.76   $96.75   $96.80  
  Purchase #4 $193.38   11.443%   $215.5085   $215.51   $215.50   $215.50  
  Purchase #5 $20.76   6.215%   $22.0502   $22.05   $22.05   $22.10  
  Purchase #6 $59.30   9.791%   $65.1061   $65.11   $65.10   $65.10  
  Purchase #7 $222.86   4.406%   $232.6792   $232.68   $232.70   $232.70  
  7 purchase totals = $831.08       $897.4065   $897.41   $897.40   $897.50