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 $247.67   5.868%   $262.2033   $262.20   $262.20   $262.20  
  Purchase #2 $189.56   10.802%   $210.0363   $210.04   $210.05   $210.00  
  Purchase #3 $157.64   5.764%   $166.7264   $166.73   $166.75   $166.70  
  Purchase #4 $129.37   11.352%   $144.0561   $144.06   $144.05   $144.10  
  Purchase #5 $223.41   4.562%   $233.602   $233.60   $233.60   $233.60  
  Purchase #6 $204.31   4.556%   $213.6184   $213.62   $213.60   $213.60  
  Purchase #7 $52.52   7.139%   $56.2694   $56.27   $56.25   $56.30  
  7 purchase totals = $1,204.48       $1,286.5119   $1,286.52   $1,286.50   $1,286.50