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 $55.44   13.384%   $62.8601   $62.86   $62.85   $62.90  
  Purchase #2 $117.99   12.717%   $132.9948   $132.99   $133.00   $133.00  
  Purchase #3 $35.69   7.372%   $38.3211   $38.32   $38.30   $38.30  
  Purchase #4 $116.51   8.807%   $126.771   $126.77   $126.75   $126.80  
  Purchase #5 $69.51   13.224%   $78.702   $78.70   $78.70   $78.70  
  Purchase #6 $74.57   10.747%   $82.584   $82.58   $82.60   $82.60  
  Purchase #7 $149.98   11.407%   $167.0882   $167.09   $167.10   $167.10  
  7 purchase totals = $619.69       $689.3212   $689.31   $689.30   $689.40