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 $36.46   6.446%   $38.8102   $38.81   $38.80   $38.80  
  Purchase #2 $158.93   4.858%   $166.6508   $166.65   $166.65   $166.70  
  Purchase #3 $70.29   8.346%   $76.1564   $76.16   $76.15   $76.20  
  Purchase #4 $205.41   10.716%   $227.4217   $227.42   $227.40   $227.40  
  Purchase #5 $23.32   9.237%   $25.4741   $25.47   $25.45   $25.50  
  Purchase #6 $165.69   4.864%   $173.7492   $173.75   $173.75   $173.70  
  Purchase #7 $57.35   6.367%   $61.0015   $61.00   $61.00   $61.00  
  7 purchase totals = $717.45       $769.2639   $769.26   $769.20   $769.30