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 $209.37   5.202%   $220.2614   $220.26   $220.25   $220.30  
  Purchase #2 $167.68   8.455%   $181.8573   $181.86   $181.85   $181.90  
  Purchase #3 $84.58   7.379%   $90.8212   $90.82   $90.80   $90.80  
  Purchase #4 $118.98   11.355%   $132.4902   $132.49   $132.50   $132.50  
  Purchase #5 $231.57   7.676%   $249.3453   $249.35   $249.35   $249.30  
  Purchase #6 $216.94   6.158%   $230.2992   $230.30   $230.30   $230.30  
  Purchase #7 $227.37   6.179%   $241.4192   $241.42   $241.40   $241.40  
  7 purchase totals = $1,256.49       $1,346.4938   $1,346.50   $1,346.45   $1,346.50