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 $212.32   9.343%   $232.1571   $232.16   $232.15   $232.20  
  Purchase #2 $248.86   7.234%   $266.8625   $266.86   $266.85   $266.90  
  Purchase #3 $64.67   5.300%   $68.0975   $68.10   $68.10   $68.10  
  Purchase #4 $175.65   9.330%   $192.0381   $192.04   $192.05   $192.00  
  Purchase #5 $231.37   6.150%   $245.5993   $245.60   $245.60   $245.60  
  Purchase #6 $243.74   10.343%   $268.95   $268.95   $268.95   $269.00  
  Purchase #7 $24.43   5.168%   $25.6925   $25.69   $25.70   $25.70  
  7 purchase totals = $1,201.04       $1,299.3970   $1,299.40   $1,299.40   $1,299.50