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 $223.75   6.243%   $237.7187   $237.72   $237.70   $237.70  
  Purchase #2 $127.32   10.291%   $140.4225   $140.42   $140.40   $140.40  
  Purchase #3 $118.98   11.130%   $132.2225   $132.22   $132.20   $132.20  
  Purchase #4 $190.91   11.236%   $212.3606   $212.36   $212.35   $212.40  
  Purchase #5 $86.95   7.159%   $93.1748   $93.17   $93.15   $93.20  
  Purchase #6 $82.96   5.766%   $87.7435   $87.74   $87.75   $87.70  
  Purchase #7 $115.41   13.714%   $131.2373   $131.24   $131.25   $131.20  
  7 purchase totals = $946.28       $1,034.8799   $1,034.87   $1,034.80   $1,034.80