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 $61.81   11.222%   $68.7463   $68.75   $68.75   $68.70  
  Purchase #2 $129.41   9.689%   $141.9485   $141.95   $141.95   $141.90  
  Purchase #3 $75.83   5.701%   $80.1531   $80.15   $80.15   $80.20  
  Purchase #4 $217.51   13.509%   $246.8934   $246.89   $246.90   $246.90  
  Purchase #5 $116.70   4.221%   $121.6259   $121.63   $121.65   $121.60  
  Purchase #6 $99.79   13.428%   $113.1898   $113.19   $113.20   $113.20  
  Purchase #7 $65.81   9.152%   $71.8329   $71.83   $71.85   $71.80  
  7 purchase totals = $766.86       $844.3899   $844.39   $844.45   $844.30