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 $60.93   9.103%   $66.4765   $66.48   $66.50   $66.50  
  Purchase #2 $240.47   5.363%   $253.3664   $253.37   $253.35   $253.40  
  Purchase #3 $44.74   8.401%   $48.4986   $48.50   $48.50   $48.50  
  Purchase #4 $110.49   11.390%   $123.0748   $123.07   $123.05   $123.10  
  Purchase #5 $180.96   3.379%   $187.0746   $187.07   $187.05   $187.10  
  Purchase #6 $126.28   8.207%   $136.6438   $136.64   $136.65   $136.60  
  Purchase #7 $229.69   9.298%   $251.0466   $251.05   $251.05   $251.00  
  7 purchase totals = $993.56       $1,066.1813   $1,066.18   $1,066.15   $1,066.20