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 $223.26   11.216%   $248.3008   $248.30   $248.30   $248.30  
  Purchase #2 $209.84   10.663%   $232.2152   $232.22   $232.20   $232.20  
  Purchase #3 $24.83   6.614%   $26.4723   $26.47   $26.45   $26.50  
  Purchase #4 $184.27   8.464%   $199.8666   $199.87   $199.85   $199.90  
  Purchase #5 $14.37   7.300%   $15.419   $15.42   $15.40   $15.40  
  Purchase #6 $88.55   5.853%   $93.7328   $93.73   $93.75   $93.70  
  Purchase #7 $215.36   6.412%   $229.1689   $229.17   $229.15   $229.20  
  7 purchase totals = $960.48       $1,045.1756   $1,045.18   $1,045.10   $1,045.20