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 $43.29   13.614%   $49.1835   $49.18   $49.20   $49.20  
  Purchase #2 $201.91   7.428%   $216.9079   $216.91   $216.90   $216.90  
  Purchase #3 $119.89   10.506%   $132.4856   $132.49   $132.50   $132.50  
  Purchase #4 $171.45   3.286%   $177.0838   $177.08   $177.10   $177.10  
  Purchase #5 $149.27   7.257%   $160.1025   $160.10   $160.10   $160.10  
  Purchase #6 $136.68   4.597%   $142.9632   $142.96   $142.95   $143.00  
  Purchase #7 $182.67   3.439%   $188.952   $188.95   $188.95   $189.00  
  7 purchase totals = $1,005.16       $1,067.6785   $1,067.67   $1,067.70   $1,067.80