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 $216.26   11.775%   $241.7246   $241.72   $241.70   $241.70  
  Purchase #2 $109.29   9.741%   $119.9359   $119.94   $119.95   $119.90  
  Purchase #3 $117.66   11.217%   $130.8579   $130.86   $130.85   $130.90  
  Purchase #4 $82.39   6.646%   $87.8656   $87.87   $87.85   $87.90  
  Purchase #5 $214.51   3.433%   $221.8741   $221.87   $221.85   $221.90  
  Purchase #6 $199.62   10.357%   $220.2946   $220.29   $220.30   $220.30  
  Purchase #7 $149.54   8.320%   $161.9817   $161.98   $162.00   $162.00  
  7 purchase totals = $1,089.27       $1,184.5344   $1,184.53   $1,184.50   $1,184.60