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 $182.32   10.781%   $201.9759   $201.98   $202.00   $202.00  
  Purchase #2 $53.47   4.701%   $55.9836   $55.98   $56.00   $56.00  
  Purchase #3 $5.90   9.758%   $6.4757   $6.48   $6.50   $6.50  
  Purchase #4 $84.79   4.168%   $88.324   $88.32   $88.30   $88.30  
  Purchase #5 $206.40   10.321%   $227.7025   $227.70   $227.70   $227.70  
  Purchase #6 $25.99   6.711%   $27.7342   $27.73   $27.75   $27.70  
  Purchase #7 $202.77   5.691%   $214.3096   $214.31   $214.30   $214.30  
  7 purchase totals = $761.64       $822.5055   $822.50   $822.55   $822.50