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 $134.71   8.781%   $146.5389   $146.54   $146.55   $146.50  
  Purchase #2 $150.85   10.706%   $167   $167.00   $167.00   $167.00  
  Purchase #3 $248.77   4.183%   $259.176   $259.18   $259.20   $259.20  
  Purchase #4 $193.69   3.159%   $199.8087   $199.81   $199.80   $199.80  
  Purchase #5 $236.88   11.415%   $263.9199   $263.92   $263.90   $263.90  
  Purchase #6 $123.92   11.848%   $138.602   $138.60   $138.60   $138.60  
  Purchase #7 $174.51   8.197%   $188.8146   $188.81   $188.80   $188.80  
  7 purchase totals = $1,263.33       $1,363.8601   $1,363.86   $1,363.85   $1,363.80