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 $65.56   6.145%   $69.5887   $69.59   $69.60   $69.60  
  Purchase #2 $244.64   11.151%   $271.9198   $271.92   $271.90   $271.90  
  Purchase #3 $95.78   7.666%   $103.1225   $103.12   $103.10   $103.10  
  Purchase #4 $141.41   6.419%   $150.4871   $150.49   $150.50   $150.50  
  Purchase #5 $93.56   3.201%   $96.5549   $96.55   $96.55   $96.60  
  Purchase #6 $214.41   4.559%   $224.185   $224.19   $224.20   $224.20  
  Purchase #7 $8.25   12.585%   $9.2883   $9.29   $9.30   $9.30  
  7 purchase totals = $863.61       $925.1463   $925.15   $925.15   $925.20