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 $233.33   10.677%   $258.2426   $258.24   $258.25   $258.20  
  Purchase #2 $182.86   13.596%   $207.7216   $207.72   $207.70   $207.70  
  Purchase #3 $246.83   10.265%   $272.1671   $272.17   $272.15   $272.20  
  Purchase #4 $64.64   6.643%   $68.934   $68.93   $68.95   $68.90  
  Purchase #5 $216.94   12.166%   $243.3329   $243.33   $243.35   $243.30  
  Purchase #6 $7.25   13.783%   $8.2493   $8.25   $8.25   $8.20  
  Purchase #7 $9.77   4.769%   $10.2359   $10.24   $10.25   $10.20  
  7 purchase totals = $961.62       $1,068.8834   $1,068.88   $1,068.90   $1,068.70