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 $151.93   7.114%   $162.7383   $162.74   $162.75   $162.70  
  Purchase #2 $170.95   9.256%   $186.7731   $186.77   $186.75   $186.80  
  Purchase #3 $150.63   12.856%   $169.995   $170.00   $170.00   $170.00  
  Purchase #4 $234.95   11.651%   $262.324   $262.32   $262.30   $262.30  
  Purchase #5 $43.58   12.867%   $49.1874   $49.19   $49.20   $49.20  
  Purchase #6 $85.91   13.562%   $97.5611   $97.56   $97.55   $97.60  
  Purchase #7 $187.58   9.175%   $204.7905   $204.79   $204.80   $204.80  
  7 purchase totals = $1,025.53       $1,133.3694   $1,133.37   $1,133.35   $1,133.40