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 $64.35   6.117%   $68.2863   $68.29   $68.30   $68.30  
  Purchase #2 $159.39   10.827%   $176.6472   $176.65   $176.65   $176.60  
  Purchase #3 $189.82   6.741%   $202.6158   $202.62   $202.60   $202.60  
  Purchase #4 $164.85   9.180%   $179.9832   $179.98   $180.00   $180.00  
  Purchase #5 $79.95   8.158%   $86.4723   $86.47   $86.45   $86.50  
  Purchase #6 $209.30   12.240%   $234.9183   $234.92   $234.90   $234.90  
  Purchase #7 $91.31   7.125%   $97.8158   $97.82   $97.80   $97.80  
  7 purchase totals = $958.97       $1,046.7389   $1,046.75   $1,046.70   $1,046.70