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 $60.26   6.204%   $63.9985   $64.00   $64.00   $64.00  
  Purchase #2 $214.39   6.233%   $227.7529   $227.75   $227.75   $227.80  
  Purchase #3 $188.34   3.442%   $194.8227   $194.82   $194.80   $194.80  
  Purchase #4 $86.95   9.404%   $95.1268   $95.13   $95.15   $95.10  
  Purchase #5 $106.28   11.463%   $118.4629   $118.46   $118.45   $118.50  
  Purchase #6 $131.89   12.646%   $148.5688   $148.57   $148.55   $148.60  
  Purchase #7 $243.77   12.243%   $273.6148   $273.61   $273.60   $273.60  
  7 purchase totals = $1,031.88       $1,122.3474   $1,122.34   $1,122.30   $1,122.40