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 $64.54   10.231%   $71.1431   $71.14   $71.15   $71.10  
  Purchase #2 $240.80   9.156%   $262.8476   $262.85   $262.85   $262.80  
  Purchase #3 $39.64   9.203%   $43.2881   $43.29   $43.30   $43.30  
  Purchase #4 $45.44   9.293%   $49.6627   $49.66   $49.65   $49.70  
  Purchase #5 $77.46   6.238%   $82.292   $82.29   $82.30   $82.30  
  Purchase #6 $233.86   13.626%   $265.7258   $265.73   $265.75   $265.70  
  Purchase #7 $23.57   13.525%   $26.7578   $26.76   $26.75   $26.80  
  7 purchase totals = $725.31       $801.7171   $801.72   $801.75   $801.70