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 $61.50   12.182%   $68.9919   $68.99   $69.00   $69.00  
  Purchase #2 $170.79   6.475%   $181.8487   $181.85   $181.85   $181.80  
  Purchase #3 $232.90   8.795%   $253.3836   $253.38   $253.40   $253.40  
  Purchase #4 $243.90   11.487%   $271.9168   $271.92   $271.90   $271.90  
  Purchase #5 $169.92   10.215%   $187.2773   $187.28   $187.30   $187.30  
  Purchase #6 $200.78   10.351%   $221.5627   $221.56   $221.55   $221.60  
  Purchase #7 $78.83   9.149%   $86.0422   $86.04   $86.05   $86.00  
  7 purchase totals = $1,158.62       $1,271.0232   $1,271.02   $1,271.05   $1,271.00