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 $246.78   9.816%   $271.0039   $271.00   $271.00   $271.00  
  Purchase #2 $206.29   3.722%   $213.9681   $213.97   $213.95   $214.00  
  Purchase #3 $116.70   13.585%   $132.5537   $132.55   $132.55   $132.60  
  Purchase #4 $86.69   10.795%   $96.0482   $96.05   $96.05   $96.00  
  Purchase #5 $98.37   11.521%   $109.7032   $109.70   $109.70   $109.70  
  Purchase #6 $132.81   8.643%   $144.2888   $144.29   $144.30   $144.30  
  Purchase #7 $53.58   7.454%   $57.5739   $57.57   $57.55   $57.60  
  7 purchase totals = $941.22       $1,025.1398   $1,025.13   $1,025.10   $1,025.20