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 $104.82   8.131%   $113.3429   $113.34   $113.35   $113.30  
  Purchase #2 $168.81   9.417%   $184.7068   $184.71   $184.70   $184.70  
  Purchase #3 $187.86   10.241%   $207.0987   $207.10   $207.10   $207.10  
  Purchase #4 $107.34   7.827%   $115.7415   $115.74   $115.75   $115.70  
  Purchase #5 $85.96   4.267%   $89.6279   $89.63   $89.65   $89.60  
  Purchase #6 $82.62   11.301%   $91.9569   $91.96   $91.95   $92.00  
  Purchase #7 $108.56   7.637%   $116.8507   $116.85   $116.85   $116.90  
  7 purchase totals = $845.97       $919.3254   $919.33   $919.35   $919.30