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 $58.87   8.728%   $64.0082   $64.01   $64.00   $64.00  
  Purchase #2 $228.63   9.765%   $250.9557   $250.96   $250.95   $251.00  
  Purchase #3 $226.94   4.710%   $237.6289   $237.63   $237.65   $237.60  
  Purchase #4 $246.87   3.250%   $254.8933   $254.89   $254.90   $254.90  
  Purchase #5 $52.87   11.126%   $58.7523   $58.75   $58.75   $58.80  
  Purchase #6 $106.39   10.483%   $117.5429   $117.54   $117.55   $117.50  
  Purchase #7 $234.55   12.499%   $263.8664   $263.87   $263.85   $263.90  
  7 purchase totals = $1,155.12       $1,247.6477   $1,247.65   $1,247.65   $1,247.70