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 $106.90   9.193%   $116.7273   $116.73   $116.75   $116.70  
  Purchase #2 $147.75   5.263%   $155.5261   $155.53   $155.55   $155.50  
  Purchase #3 $37.54   6.102%   $39.8307   $39.83   $39.85   $39.80  
  Purchase #4 $71.89   6.444%   $76.5226   $76.52   $76.50   $76.50  
  Purchase #5 $200.28   3.173%   $206.6349   $206.63   $206.65   $206.60  
  Purchase #6 $41.42   12.556%   $46.6207   $46.62   $46.60   $46.60  
  Purchase #7 $170.77   11.461%   $190.3419   $190.34   $190.35   $190.30  
  7 purchase totals = $776.55       $832.2042   $832.20   $832.25   $832.00