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 $119.79   5.738%   $126.6636   $126.66   $126.65   $126.70  
  Purchase #2 $110.88   5.281%   $116.7356   $116.74   $116.75   $116.70  
  Purchase #3 $54.25   5.854%   $57.4258   $57.43   $57.45   $57.40  
  Purchase #4 $103.85   9.303%   $113.5112   $113.51   $113.50   $113.50  
  Purchase #5 $125.89   12.265%   $141.3304   $141.33   $141.35   $141.30  
  Purchase #6 $214.64   12.161%   $240.7424   $240.74   $240.75   $240.70  
  Purchase #7 $159.45   10.732%   $176.5622   $176.56   $176.55   $176.60  
  7 purchase totals = $888.75       $972.9712   $972.97   $973.00   $972.90