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 $96.36   5.154%   $101.3264   $101.33   $101.35   $101.30  
  Purchase #2 $223.86   4.498%   $233.9292   $233.93   $233.95   $233.90  
  Purchase #3 $244.47   12.497%   $275.0214   $275.02   $275.00   $275.00  
  Purchase #4 $225.76   3.573%   $233.8264   $233.83   $233.85   $233.80  
  Purchase #5 $90.39   4.391%   $94.359   $94.36   $94.35   $94.40  
  Purchase #6 $9.48   4.394%   $9.8966   $9.90   $9.90   $9.90  
  Purchase #7 $173.71   9.224%   $189.733   $189.73   $189.75   $189.70  
  7 purchase totals = $1,064.03       $1,138.0920   $1,138.10   $1,138.15   $1,138.00