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 $106.58   11.311%   $118.6353   $118.64   $118.65   $118.60  
  Purchase #2 $148.82   5.732%   $157.3504   $157.35   $157.35   $157.40  
  Purchase #3 $199.69   8.341%   $216.3461   $216.35   $216.35   $216.30  
  Purchase #4 $168.99   5.443%   $178.1881   $178.19   $178.20   $178.20  
  Purchase #5 $162.27   11.466%   $180.8759   $180.88   $180.90   $180.90  
  Purchase #6 $83.47   11.230%   $92.8437   $92.84   $92.85   $92.80  
  Purchase #7 $123.36   5.402%   $130.0239   $130.02   $130.00   $130.00  
  7 purchase totals = $993.18       $1,074.2634   $1,074.27   $1,074.30   $1,074.20