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 $183.44   6.532%   $195.4223   $195.42   $195.40   $195.40  
  Purchase #2 $33.57   5.377%   $35.3751   $35.38   $35.40   $35.40  
  Purchase #3 $156.45   9.188%   $170.8246   $170.82   $170.80   $170.80  
  Purchase #4 $168.83   4.625%   $176.6384   $176.64   $176.65   $176.60  
  Purchase #5 $222.47   4.851%   $233.262   $233.26   $233.25   $233.30  
  Purchase #6 $70.75   10.444%   $78.1391   $78.14   $78.15   $78.10  
  Purchase #7 $151.52   12.695%   $170.7555   $170.76   $170.75   $170.80  
  7 purchase totals = $987.03       $1,060.4170   $1,060.42   $1,060.40   $1,060.40