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 $62.83   13.849%   $71.5313   $71.53   $71.55   $71.50  
  Purchase #2 $96.34   4.207%   $100.393   $100.39   $100.40   $100.40  
  Purchase #3 $108.52   9.384%   $118.7035   $118.70   $118.70   $118.70  
  Purchase #4 $238.29   11.287%   $265.1858   $265.19   $265.20   $265.20  
  Purchase #5 $15.44   6.741%   $16.4808   $16.48   $16.50   $16.50  
  Purchase #6 $169.77   5.508%   $179.1209   $179.12   $179.10   $179.10  
  Purchase #7 $193.50   11.591%   $215.9286   $215.93   $215.95   $215.90  
  7 purchase totals = $884.69       $967.3439   $967.34   $967.40   $967.30