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 $31.49   8.224%   $34.0797   $34.08   $34.10   $34.10  
  Purchase #2 $234.36   5.564%   $247.3998   $247.40   $247.40   $247.40  
  Purchase #3 $115.37   8.408%   $125.0703   $125.07   $125.05   $125.10  
  Purchase #4 $64.85   5.790%   $68.6048   $68.60   $68.60   $68.60  
  Purchase #5 $247.25   5.153%   $259.9908   $259.99   $260.00   $260.00  
  Purchase #6 $10.73   9.598%   $11.7599   $11.76   $11.75   $11.80  
  Purchase #7 $81.63   6.782%   $87.1661   $87.17   $87.15   $87.20  
  7 purchase totals = $785.68       $834.0714   $834.07   $834.05   $834.20