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 $52.74   9.699%   $57.8553   $57.86   $57.85   $57.90  
  Purchase #2 $56.66   11.219%   $63.0167   $63.02   $63.00   $63.00  
  Purchase #3 $136.46   9.701%   $149.698   $149.70   $149.70   $149.70  
  Purchase #4 $20.30   8.483%   $22.022   $22.02   $22.00   $22.00  
  Purchase #5 $132.38   4.127%   $137.8433   $137.84   $137.85   $137.80  
  Purchase #6 $59.36   8.215%   $64.2364   $64.24   $64.25   $64.20  
  Purchase #7 $229.54   9.752%   $251.9247   $251.92   $251.90   $251.90  
  7 purchase totals = $687.44       $746.5964   $746.60   $746.55   $746.50