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 $219.76   12.823%   $247.9398   $247.94   $247.95   $247.90  
  Purchase #2 $168.42   5.799%   $178.1867   $178.19   $178.20   $178.20  
  Purchase #3 $206.51   4.336%   $215.4643   $215.46   $215.45   $215.50  
  Purchase #4 $63.42   9.152%   $69.2242   $69.22   $69.20   $69.20  
  Purchase #5 $235.58   13.598%   $267.6142   $267.61   $267.60   $267.60  
  Purchase #6 $155.47   12.470%   $174.8571   $174.86   $174.85   $174.90  
  Purchase #7 $101.96   6.425%   $108.5109   $108.51   $108.50   $108.50  
  7 purchase totals = $1,151.12       $1,261.7972   $1,261.79   $1,261.75   $1,261.80