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 $75.57   9.416%   $82.6857   $82.69   $82.70   $82.70  
  Purchase #2 $71.32   4.248%   $74.3497   $74.35   $74.35   $74.30  
  Purchase #3 $83.50   8.128%   $90.2869   $90.29   $90.30   $90.30  
  Purchase #4 $89.26   11.849%   $99.8364   $99.84   $99.85   $99.80  
  Purchase #5 $234.66   3.177%   $242.1151   $242.12   $242.10   $242.10  
  Purchase #6 $183.60   10.433%   $202.755   $202.76   $202.75   $202.80  
  Purchase #7 $59.31   10.658%   $65.6313   $65.63   $65.65   $65.60  
  7 purchase totals = $797.22       $857.6601   $857.68   $857.70   $857.60