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 $242.26   6.230%   $257.3528   $257.35   $257.35   $257.40  
  Purchase #2 $168.88   6.386%   $179.6647   $179.66   $179.65   $179.70  
  Purchase #3 $53.74   9.743%   $58.9759   $58.98   $59.00   $59.00  
  Purchase #4 $217.35   11.511%   $242.3692   $242.37   $242.35   $242.40  
  Purchase #5 $130.34   6.113%   $138.3077   $138.31   $138.30   $138.30  
  Purchase #6 $80.27   10.313%   $88.5482   $88.55   $88.55   $88.50  
  Purchase #7 $119.75   9.167%   $130.7275   $130.73   $130.75   $130.70  
  7 purchase totals = $1,012.59       $1,095.9460   $1,095.95   $1,095.95   $1,096.00