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 $246.59   8.354%   $267.1901   $267.19   $267.20   $267.20  
  Purchase #2 $125.57   12.347%   $141.0741   $141.07   $141.05   $141.10  
  Purchase #3 $68.58   13.319%   $77.7142   $77.71   $77.70   $77.70  
  Purchase #4 $94.34   4.781%   $98.8504   $98.85   $98.85   $98.90  
  Purchase #5 $66.31   4.135%   $69.0519   $69.05   $69.05   $69.10  
  Purchase #6 $42.55   7.176%   $45.6034   $45.60   $45.60   $45.60  
  Purchase #7 $142.50   7.645%   $153.3941   $153.39   $153.40   $153.40  
  7 purchase totals = $786.44       $852.8782   $852.86   $852.85   $853.00