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 $234.60   5.169%   $246.7265   $246.73   $246.75   $246.70  
  Purchase #2 $91.83   3.572%   $95.1102   $95.11   $95.10   $95.10  
  Purchase #3 $71.55   4.306%   $74.6309   $74.63   $74.65   $74.60  
  Purchase #4 $243.65   5.605%   $257.3066   $257.31   $257.30   $257.30  
  Purchase #5 $211.42   11.698%   $236.1519   $236.15   $236.15   $236.20  
  Purchase #6 $137.95   11.618%   $153.977   $153.98   $154.00   $154.00  
  Purchase #7 $112.50   4.611%   $117.6874   $117.69   $117.70   $117.70  
  7 purchase totals = $1,103.50       $1,181.5905   $1,181.60   $1,181.65   $1,181.60