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 $55.95   12.551%   $62.9723   $62.97   $62.95   $63.00  
  Purchase #2 $221.91   7.684%   $238.9616   $238.96   $238.95   $239.00  
  Purchase #3 $57.88   5.790%   $61.2313   $61.23   $61.25   $61.20  
  Purchase #4 $178.55   3.581%   $184.9439   $184.94   $184.95   $184.90  
  Purchase #5 $31.56   8.635%   $34.2852   $34.29   $34.30   $34.30  
  Purchase #6 $202.84   7.334%   $217.7163   $217.72   $217.70   $217.70  
  Purchase #7 $86.39   7.459%   $92.8338   $92.83   $92.85   $92.80  
  7 purchase totals = $835.08       $892.9444   $892.94   $892.95   $892.90