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 $60.93   10.594%   $67.3849   $67.38   $67.40   $67.40  
  Purchase #2 $36.39   7.557%   $39.14   $39.14   $39.15   $39.10  
  Purchase #3 $7.44   10.235%   $8.2015   $8.20   $8.20   $8.20  
  Purchase #4 $55.80   10.227%   $61.5067   $61.51   $61.50   $61.50  
  Purchase #5 $84.48   13.823%   $96.1577   $96.16   $96.15   $96.20  
  Purchase #6 $118.89   6.778%   $126.9484   $126.95   $126.95   $126.90  
  Purchase #7 $134.51   7.765%   $144.9547   $144.95   $144.95   $145.00  
  7 purchase totals = $498.44       $544.2939   $544.29   $544.30   $544.30