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 $193.86   6.112%   $205.7087   $205.71   $205.70   $205.70  
  Purchase #2 $21.39   6.389%   $22.7566   $22.76   $22.75   $22.80  
  Purchase #3 $69.74   9.364%   $76.2705   $76.27   $76.25   $76.30  
  Purchase #4 $236.81   12.846%   $267.2306   $267.23   $267.25   $267.20  
  Purchase #5 $63.75   5.616%   $67.3302   $67.33   $67.35   $67.30  
  Purchase #6 $176.67   10.720%   $195.609   $195.61   $195.60   $195.60  
  Purchase #7 $119.71   11.107%   $133.0062   $133.01   $133.00   $133.00  
  7 purchase totals = $881.93       $967.9118   $967.92   $967.90   $967.90