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 $194.78   11.275%   $216.7414   $216.74   $216.75   $216.70  
  Purchase #2 $125.71   6.471%   $133.8447   $133.84   $133.85   $133.80  
  Purchase #3 $166.86   5.699%   $176.3694   $176.37   $176.35   $176.40  
  Purchase #4 $173.27   11.551%   $193.2844   $193.28   $193.30   $193.30  
  Purchase #5 $85.80   11.212%   $95.4199   $95.42   $95.40   $95.40  
  Purchase #6 $135.36   5.133%   $142.308   $142.31   $142.30   $142.30  
  Purchase #7 $55.32   9.191%   $60.4045   $60.40   $60.40   $60.40  
  7 purchase totals = $937.10       $1,018.3723   $1,018.36   $1,018.35   $1,018.30