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 $111.88   11.264%   $124.4822   $124.48   $124.50   $124.50  
  Purchase #2 $102.84   13.638%   $116.8653   $116.87   $116.85   $116.90  
  Purchase #3 $19.44   6.399%   $20.684   $20.68   $20.70   $20.70  
  Purchase #4 $204.97   4.149%   $213.4742   $213.47   $213.45   $213.50  
  Purchase #5 $217.81   7.483%   $234.1087   $234.11   $234.10   $234.10  
  Purchase #6 $107.37   11.309%   $119.5125   $119.51   $119.50   $119.50  
  Purchase #7 $207.28   12.634%   $233.4678   $233.47   $233.45   $233.50  
  7 purchase totals = $971.59       $1,062.5947   $1,062.59   $1,062.55   $1,062.70