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 $232.76   6.197%   $247.1841   $247.18   $247.20   $247.20  
  Purchase #2 $84.73   13.286%   $95.9872   $95.99   $96.00   $96.00  
  Purchase #3 $92.26   4.378%   $96.2991   $96.30   $96.30   $96.30  
  Purchase #4 $110.29   6.820%   $117.8118   $117.81   $117.80   $117.80  
  Purchase #5 $153.80   6.610%   $163.9662   $163.97   $163.95   $164.00  
  Purchase #6 $226.34   7.122%   $242.4599   $242.46   $242.45   $242.50  
  Purchase #7 $75.31   4.240%   $78.5031   $78.50   $78.50   $78.50  
  7 purchase totals = $975.49       $1,042.2114   $1,042.21   $1,042.20   $1,042.30