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 $210.49   12.417%   $236.6265   $236.63   $236.65   $236.60  
  Purchase #2 $67.48   11.375%   $75.1559   $75.16   $75.15   $75.20  
  Purchase #3 $107.27   7.828%   $115.6671   $115.67   $115.65   $115.70  
  Purchase #4 $200.68   10.292%   $221.334   $221.33   $221.35   $221.30  
  Purchase #5 $61.49   13.127%   $69.5618   $69.56   $69.55   $69.60  
  Purchase #6 $145.55   6.103%   $154.4329   $154.43   $154.45   $154.40  
  Purchase #7 $83.42   4.240%   $86.957   $86.96   $86.95   $87.00  
  7 purchase totals = $876.38       $959.7352   $959.74   $959.75   $959.80