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 $69.27   12.427%   $77.8782   $77.88   $77.90   $77.90  
  Purchase #2 $180.79   7.778%   $194.8518   $194.85   $194.85   $194.90  
  Purchase #3 $213.70   12.188%   $239.7458   $239.75   $239.75   $239.70  
  Purchase #4 $206.72   12.778%   $233.1347   $233.13   $233.15   $233.10  
  Purchase #5 $239.34   9.593%   $262.2999   $262.30   $262.30   $262.30  
  Purchase #6 $202.85   7.826%   $218.725   $218.73   $218.75   $218.70  
  Purchase #7 $75.59   8.495%   $82.0114   $82.01   $82.00   $82.00  
  7 purchase totals = $1,188.26       $1,308.6468   $1,308.65   $1,308.70   $1,308.60