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 $202.35   4.234%   $210.9175   $210.92   $210.90   $210.90  
  Purchase #2 $119.99   8.631%   $130.3463   $130.35   $130.35   $130.30  
  Purchase #3 $31.33   11.508%   $34.9355   $34.94   $34.95   $34.90  
  Purchase #4 $38.28   8.375%   $41.486   $41.49   $41.50   $41.50  
  Purchase #5 $84.47   7.257%   $90.6   $90.60   $90.60   $90.60  
  Purchase #6 $146.98   11.302%   $163.5917   $163.59   $163.60   $163.60  
  Purchase #7 $24.27   9.121%   $26.4837   $26.48   $26.50   $26.50  
  7 purchase totals = $647.67       $698.3607   $698.37   $698.40   $698.30