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 $231.85   6.638%   $247.2402   $247.24   $247.25   $247.20  
  Purchase #2 $92.57   4.514%   $96.7486   $96.75   $96.75   $96.70  
  Purchase #3 $204.96   5.237%   $215.6938   $215.69   $215.70   $215.70  
  Purchase #4 $137.85   10.702%   $152.6027   $152.60   $152.60   $152.60  
  Purchase #5 $169.48   12.805%   $191.1819   $191.18   $191.20   $191.20  
  Purchase #6 $132.92   6.760%   $141.9054   $141.91   $141.90   $141.90  
  Purchase #7 $167.83   11.616%   $187.3251   $187.33   $187.35   $187.30  
  7 purchase totals = $1,137.46       $1,232.6977   $1,232.70   $1,232.75   $1,232.60