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 $213.55   11.441%   $237.9823   $237.98   $238.00   $238.00  
  Purchase #2 $217.42   10.846%   $241.0014   $241.00   $241.00   $241.00  
  Purchase #3 $115.52   11.559%   $128.873   $128.87   $128.85   $128.90  
  Purchase #4 $179.42   11.856%   $200.692   $200.69   $200.70   $200.70  
  Purchase #5 $127.76   3.773%   $132.5804   $132.58   $132.60   $132.60  
  Purchase #6 $51.39   3.184%   $53.0263   $53.03   $53.05   $53.00  
  Purchase #7 $126.99   11.206%   $141.2205   $141.22   $141.20   $141.20  
  7 purchase totals = $1,032.05       $1,135.3759   $1,135.37   $1,135.40   $1,135.40