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 $233.62   12.583%   $263.0164   $263.02   $263.00   $263.00  
  Purchase #2 $23.62   4.228%   $24.6187   $24.62   $24.60   $24.60  
  Purchase #3 $113.63   3.374%   $117.4639   $117.46   $117.45   $117.50  
  Purchase #4 $206.68   5.507%   $218.0619   $218.06   $218.05   $218.10  
  Purchase #5 $97.88   9.119%   $106.8057   $106.81   $106.80   $106.80  
  Purchase #6 $25.58   8.635%   $27.7888   $27.79   $27.80   $27.80  
  Purchase #7 $243.99   5.637%   $257.7437   $257.74   $257.75   $257.70  
  7 purchase totals = $945.00       $1,015.4991   $1,015.50   $1,015.45   $1,015.50