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 $236.29   8.204%   $255.6752   $255.68   $255.70   $255.70  
  Purchase #2 $21.51   13.201%   $24.3495   $24.35   $24.35   $24.30  
  Purchase #3 $226.36   13.687%   $257.3419   $257.34   $257.35   $257.30  
  Purchase #4 $190.39   4.125%   $198.2436   $198.24   $198.25   $198.20  
  Purchase #5 $208.71   9.407%   $228.3433   $228.34   $228.35   $228.30  
  Purchase #6 $142.98   13.273%   $161.9577   $161.96   $161.95   $162.00  
  Purchase #7 $192.89   8.658%   $209.5904   $209.59   $209.60   $209.60  
  7 purchase totals = $1,219.13       $1,335.5016   $1,335.50   $1,335.55   $1,335.40