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 $247.28   7.834%   $266.6519   $266.65   $266.65   $266.70  
  Purchase #2 $35.51   3.175%   $36.6374   $36.64   $36.65   $36.60  
  Purchase #3 $91.83   4.290%   $95.7695   $95.77   $95.75   $95.80  
  Purchase #4 $206.26   3.640%   $213.7679   $213.77   $213.75   $213.80  
  Purchase #5 $168.94   4.588%   $176.691   $176.69   $176.70   $176.70  
  Purchase #6 $212.96   13.342%   $241.3731   $241.37   $241.35   $241.40  
  Purchase #7 $27.35   8.513%   $29.6783   $29.68   $29.70   $29.70  
  7 purchase totals = $990.13       $1,060.5691   $1,060.57   $1,060.55   $1,060.70