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 $245.28   3.538%   $253.958   $253.96   $253.95   $254.00  
  Purchase #2 $159.38   8.157%   $172.3806   $172.38   $172.40   $172.40  
  Purchase #3 $172.62   4.660%   $180.6641   $180.66   $180.65   $180.70  
  Purchase #4 $175.63   10.155%   $193.4652   $193.47   $193.45   $193.50  
  Purchase #5 $180.74   6.361%   $192.2369   $192.24   $192.25   $192.20  
  Purchase #6 $213.66   9.667%   $234.3145   $234.31   $234.30   $234.30  
  Purchase #7 $138.68   3.717%   $143.8347   $143.83   $143.85   $143.80  
  7 purchase totals = $1,285.99       $1,370.8540   $1,370.85   $1,370.85   $1,370.90