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 $65.64   11.712%   $73.3278   $73.33   $73.35   $73.30  
  Purchase #2 $245.83   10.533%   $271.7233   $271.72   $271.70   $271.70  
  Purchase #3 $118.76   12.851%   $134.0218   $134.02   $134.00   $134.00  
  Purchase #4 $160.96   4.581%   $168.3336   $168.33   $168.35   $168.30  
  Purchase #5 $158.55   12.203%   $177.8979   $177.90   $177.90   $177.90  
  Purchase #6 $39.89   8.380%   $43.2328   $43.23   $43.25   $43.20  
  Purchase #7 $83.45   9.382%   $91.2793   $91.28   $91.30   $91.30  
  7 purchase totals = $873.08       $959.8165   $959.81   $959.85   $959.70