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 $238.87   6.458%   $254.2962   $254.30   $254.30   $254.30  
  Purchase #2 $98.62   4.108%   $102.6713   $102.67   $102.65   $102.70  
  Purchase #3 $176.86   10.445%   $195.333   $195.33   $195.35   $195.30  
  Purchase #4 $133.59   5.785%   $141.3182   $141.32   $141.30   $141.30  
  Purchase #5 $116.67   13.704%   $132.6585   $132.66   $132.65   $132.70  
  Purchase #6 $165.25   7.831%   $178.1907   $178.19   $178.20   $178.20  
  Purchase #7 $62.70   12.349%   $70.4428   $70.44   $70.45   $70.40  
  7 purchase totals = $992.56       $1,074.9107   $1,074.91   $1,074.90   $1,074.90