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 $32.75   8.523%   $35.5413   $35.54   $35.55   $35.50  
  Purchase #2 $141.64   12.796%   $159.7643   $159.76   $159.75   $159.80  
  Purchase #3 $228.87   11.339%   $254.8216   $254.82   $254.80   $254.80  
  Purchase #4 $202.82   4.666%   $212.2836   $212.28   $212.30   $212.30  
  Purchase #5 $171.81   6.127%   $182.3368   $182.34   $182.35   $182.30  
  Purchase #6 $88.72   4.557%   $92.763   $92.76   $92.75   $92.80  
  Purchase #7 $94.91   4.254%   $98.9475   $98.95   $98.95   $98.90  
  7 purchase totals = $961.52       $1,036.4581   $1,036.45   $1,036.45   $1,036.40