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 $245.94   8.678%   $267.2827   $267.28   $267.30   $267.30  
  Purchase #2 $75.58   12.253%   $84.8408   $84.84   $84.85   $84.80  
  Purchase #3 $153.97   12.827%   $173.7197   $173.72   $173.70   $173.70  
  Purchase #4 $215.33   3.164%   $222.143   $222.14   $222.15   $222.10  
  Purchase #5 $131.57   7.153%   $140.9812   $140.98   $141.00   $141.00  
  Purchase #6 $120.67   6.825%   $128.9057   $128.91   $128.90   $128.90  
  Purchase #7 $15.27   3.646%   $15.8267   $15.83   $15.85   $15.80  
  7 purchase totals = $958.33       $1,033.6998   $1,033.70   $1,033.75   $1,033.60