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 $206.37   13.388%   $233.9988   $234.00   $234.00   $234.00  
  Purchase #2 $81.99   5.297%   $86.333   $86.33   $86.35   $86.30  
  Purchase #3 $212.78   7.714%   $229.1938   $229.19   $229.20   $229.20  
  Purchase #4 $147.71   13.524%   $167.6863   $167.69   $167.70   $167.70  
  Purchase #5 $34.82   12.432%   $39.1488   $39.15   $39.15   $39.10  
  Purchase #6 $18.46   4.675%   $19.323   $19.32   $19.30   $19.30  
  Purchase #7 $233.56   10.729%   $258.6187   $258.62   $258.60   $258.60  
  7 purchase totals = $935.69       $1,034.3024   $1,034.30   $1,034.30   $1,034.20