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 $55.46   13.506%   $62.9504   $62.95   $62.95   $63.00  
  Purchase #2 $248.69   12.554%   $279.9105   $279.91   $279.90   $279.90  
  Purchase #3 $112.70   4.559%   $117.838   $117.84   $117.85   $117.80  
  Purchase #4 $96.94   3.228%   $100.0692   $100.07   $100.05   $100.10  
  Purchase #5 $241.49   3.360%   $249.6041   $249.60   $249.60   $249.60  
  Purchase #6 $77.79   9.446%   $85.138   $85.14   $85.15   $85.10  
  Purchase #7 $67.28   10.837%   $74.5711   $74.57   $74.55   $74.60  
  7 purchase totals = $900.35       $970.0813   $970.08   $970.05   $970.10