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 $236.25   4.215%   $246.2079   $246.21   $246.20   $246.20  
  Purchase #2 $184.38   5.706%   $194.9007   $194.90   $194.90   $194.90  
  Purchase #3 $84.39   6.351%   $89.7496   $89.75   $89.75   $89.70  
  Purchase #4 $203.69   11.102%   $226.3037   $226.30   $226.30   $226.30  
  Purchase #5 $162.26   13.197%   $183.6735   $183.67   $183.65   $183.70  
  Purchase #6 $111.32   5.283%   $117.201   $117.20   $117.20   $117.20  
  Purchase #7 $193.55   3.695%   $200.7017   $200.70   $200.70   $200.70  
  7 purchase totals = $1,175.84       $1,258.7381   $1,258.73   $1,258.70   $1,258.70