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 $119.68   12.147%   $134.2175   $134.22   $134.20   $134.20  
  Purchase #2 $194.34   7.274%   $208.4763   $208.48   $208.50   $208.50  
  Purchase #3 $125.64   6.368%   $133.6408   $133.64   $133.65   $133.60  
  Purchase #4 $204.75   7.597%   $220.3049   $220.30   $220.30   $220.30  
  Purchase #5 $86.64   9.323%   $94.7174   $94.72   $94.70   $94.70  
  Purchase #6 $48.33   5.797%   $51.1317   $51.13   $51.15   $51.10  
  Purchase #7 $174.79   9.217%   $190.9004   $190.90   $190.90   $190.90  
  7 purchase totals = $954.17       $1,033.3890   $1,033.39   $1,033.40   $1,033.30