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 $194.73   9.643%   $213.5078   $213.51   $213.50   $213.50  
  Purchase #2 $24.51   11.420%   $27.309   $27.31   $27.30   $27.30  
  Purchase #3 $109.29   7.842%   $117.8605   $117.86   $117.85   $117.90  
  Purchase #4 $246.60   12.282%   $276.8874   $276.89   $276.90   $276.90  
  Purchase #5 $163.31   3.797%   $169.5109   $169.51   $169.50   $169.50  
  Purchase #6 $86.96   10.569%   $96.1508   $96.15   $96.15   $96.20  
  Purchase #7 $163.95   7.320%   $175.9511   $175.95   $175.95   $176.00  
  7 purchase totals = $989.35       $1,077.1775   $1,077.18   $1,077.15   $1,077.30