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 $118.71   6.459%   $126.3775   $126.38   $126.40   $126.40  
  Purchase #2 $34.27   4.159%   $35.6953   $35.70   $35.70   $35.70  
  Purchase #3 $244.95   8.350%   $265.4033   $265.40   $265.40   $265.40  
  Purchase #4 $54.65   5.831%   $57.8366   $57.84   $57.85   $57.80  
  Purchase #5 $102.77   12.176%   $115.2833   $115.28   $115.30   $115.30  
  Purchase #6 $117.79   11.515%   $131.3535   $131.35   $131.35   $131.40  
  Purchase #7 $111.47   4.396%   $116.3702   $116.37   $116.35   $116.40  
  7 purchase totals = $784.61       $848.3197   $848.32   $848.35   $848.40