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 $241.98   13.722%   $275.1845   $275.18   $275.20   $275.20  
  Purchase #2 $110.93   6.820%   $118.4954   $118.50   $118.50   $118.50  
  Purchase #3 $62.51   5.322%   $65.8368   $65.84   $65.85   $65.80  
  Purchase #4 $175.50   5.567%   $185.2701   $185.27   $185.25   $185.30  
  Purchase #5 $189.98   6.462%   $202.2565   $202.26   $202.25   $202.30  
  Purchase #6 $47.52   3.641%   $49.2502   $49.25   $49.25   $49.30  
  Purchase #7 $30.95   13.706%   $35.192   $35.19   $35.20   $35.20  
  7 purchase totals = $859.37       $931.4855   $931.49   $931.50   $931.60