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 $61.44   5.281%   $64.6846   $64.68   $64.70   $64.70  
  Purchase #2 $41.51   12.429%   $46.6693   $46.67   $46.65   $46.70  
  Purchase #3 $160.82   7.315%   $172.584   $172.58   $172.60   $172.60  
  Purchase #4 $51.89   6.784%   $55.4102   $55.41   $55.40   $55.40  
  Purchase #5 $146.57   13.690%   $166.6354   $166.64   $166.65   $166.60  
  Purchase #6 $8.73   7.429%   $9.3786   $9.38   $9.40   $9.40  
  Purchase #7 $230.48   12.647%   $259.6288   $259.63   $259.65   $259.60  
  7 purchase totals = $701.44       $774.9909   $774.99   $775.05   $775.00