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 $248.69   4.792%   $260.6072   $260.61   $260.60   $260.60  
  Purchase #2 $210.95   8.842%   $229.6022   $229.60   $229.60   $229.60  
  Purchase #3 $177.60   3.112%   $183.1269   $183.13   $183.15   $183.10  
  Purchase #4 $244.26   10.253%   $269.304   $269.30   $269.30   $269.30  
  Purchase #5 $150.81   11.444%   $168.0687   $168.07   $168.05   $168.10  
  Purchase #6 $49.57   4.148%   $51.6262   $51.63   $51.65   $51.60  
  Purchase #7 $186.46   11.776%   $208.4175   $208.42   $208.40   $208.40  
  7 purchase totals = $1,268.34       $1,370.7527   $1,370.76   $1,370.75   $1,370.70