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 $85.99   11.271%   $95.6819   $95.68   $95.70   $95.70  
  Purchase #2 $186.52   7.740%   $200.9566   $200.96   $200.95   $201.00  
  Purchase #3 $146.30   13.677%   $166.3095   $166.31   $166.30   $166.30  
  Purchase #4 $42.80   4.709%   $44.8155   $44.82   $44.80   $44.80  
  Purchase #5 $91.52   3.256%   $94.4999   $94.50   $94.50   $94.50  
  Purchase #6 $215.41   11.661%   $240.529   $240.53   $240.55   $240.50  
  Purchase #7 $104.39   13.546%   $118.5307   $118.53   $118.55   $118.50  
  7 purchase totals = $872.93       $961.3231   $961.33   $961.35   $961.30