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 $124.82   10.291%   $137.6652   $137.67   $137.65   $137.70  
  Purchase #2 $78.32   8.741%   $85.166   $85.17   $85.15   $85.20  
  Purchase #3 $129.65   10.616%   $143.4136   $143.41   $143.40   $143.40  
  Purchase #4 $174.97   11.814%   $195.641   $195.64   $195.65   $195.60  
  Purchase #5 $176.95   7.366%   $189.9841   $189.98   $190.00   $190.00  
  Purchase #6 $205.56   3.829%   $213.4309   $213.43   $213.45   $213.40  
  Purchase #7 $64.31   6.475%   $68.4741   $68.47   $68.45   $68.50  
  7 purchase totals = $954.58       $1,033.7749   $1,033.77   $1,033.75   $1,033.80