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 $245.85   3.143%   $253.5771   $253.58   $253.60   $253.60  
  Purchase #2 $186.31   8.377%   $201.9172   $201.92   $201.90   $201.90  
  Purchase #3 $9.93   6.277%   $10.5533   $10.55   $10.55   $10.60  
  Purchase #4 $93.62   8.511%   $101.588   $101.59   $101.60   $101.60  
  Purchase #5 $51.46   5.765%   $54.4267   $54.43   $54.45   $54.40  
  Purchase #6 $167.87   6.231%   $178.33   $178.33   $178.35   $178.30  
  Purchase #7 $114.81   11.379%   $127.8742   $127.87   $127.85   $127.90  
  7 purchase totals = $869.85       $928.2665   $928.27   $928.30   $928.30