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 $33.65   12.226%   $37.764   $37.76   $37.75   $37.80  
  Purchase #2 $52.96   11.151%   $58.8656   $58.87   $58.85   $58.90  
  Purchase #3 $55.28   7.224%   $59.2734   $59.27   $59.25   $59.30  
  Purchase #4 $172.26   10.153%   $189.7496   $189.75   $189.75   $189.70  
  Purchase #5 $115.28   7.273%   $123.6643   $123.66   $123.65   $123.70  
  Purchase #6 $119.73   5.584%   $126.4157   $126.42   $126.40   $126.40  
  Purchase #7 $110.88   7.294%   $118.9676   $118.97   $118.95   $119.00  
  7 purchase totals = $660.04       $714.7002   $714.70   $714.60   $714.80