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 $56.54   9.642%   $61.9916   $61.99   $62.00   $62.00  
  Purchase #2 $116.43   8.243%   $126.0273   $126.03   $126.05   $126.00  
  Purchase #3 $172.32   5.730%   $182.1939   $182.19   $182.20   $182.20  
  Purchase #4 $28.30   11.385%   $31.522   $31.52   $31.50   $31.50  
  Purchase #5 $191.70   9.232%   $209.3977   $209.40   $209.40   $209.40  
  Purchase #6 $138.74   11.200%   $154.2789   $154.28   $154.30   $154.30  
  Purchase #7 $178.33   9.262%   $194.8469   $194.85   $194.85   $194.80  
  7 purchase totals = $882.36       $960.2583   $960.26   $960.30   $960.20