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 $238.76   11.139%   $265.3555   $265.36   $265.35   $265.40  
  Purchase #2 $206.93   9.386%   $226.3524   $226.35   $226.35   $226.40  
  Purchase #3 $201.30   6.150%   $213.68   $213.68   $213.70   $213.70  
  Purchase #4 $186.50   8.728%   $202.7777   $202.78   $202.80   $202.80  
  Purchase #5 $220.63   11.173%   $245.281   $245.28   $245.30   $245.30  
  Purchase #6 $62.71   3.390%   $64.8359   $64.84   $64.85   $64.80  
  Purchase #7 $90.54   4.184%   $94.3282   $94.33   $94.35   $94.30  
  7 purchase totals = $1,207.37       $1,312.6107   $1,312.62   $1,312.70   $1,312.70