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 $232.58   3.642%   $241.0506   $241.05   $241.05   $241.10  
  Purchase #2 $33.81   6.759%   $36.0952   $36.10   $36.10   $36.10  
  Purchase #3 $94.74   7.534%   $101.8777   $101.88   $101.90   $101.90  
  Purchase #4 $153.28   8.439%   $166.2153   $166.22   $166.20   $166.20  
  Purchase #5 $37.66   9.691%   $41.3096   $41.31   $41.30   $41.30  
  Purchase #6 $103.34   4.515%   $108.0058   $108.01   $108.00   $108.00  
  Purchase #7 $128.97   5.847%   $136.5109   $136.51   $136.50   $136.50  
  7 purchase totals = $784.38       $831.0651   $831.08   $831.05   $831.10