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 $203.49   11.411%   $226.7102   $226.71   $226.70   $226.70  
  Purchase #2 $183.48   6.392%   $195.208   $195.21   $195.20   $195.20  
  Purchase #3 $173.66   8.734%   $188.8275   $188.83   $188.85   $188.80  
  Purchase #4 $70.85   8.229%   $76.6802   $76.68   $76.70   $76.70  
  Purchase #5 $87.67   6.370%   $93.2546   $93.25   $93.25   $93.30  
  Purchase #6 $67.62   13.609%   $76.8224   $76.82   $76.80   $76.80  
  Purchase #7 $223.35   10.194%   $246.1183   $246.12   $246.10   $246.10  
  7 purchase totals = $1,010.12       $1,103.6212   $1,103.62   $1,103.60   $1,103.60