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 $247.69   7.638%   $266.6086   $266.61   $266.60   $266.60  
  Purchase #2 $213.57   3.830%   $221.7497   $221.75   $221.75   $221.70  
  Purchase #3 $220.50   11.330%   $245.4827   $245.48   $245.50   $245.50  
  Purchase #4 $109.86   11.221%   $122.1874   $122.19   $122.20   $122.20  
  Purchase #5 $12.72   12.829%   $14.3518   $14.35   $14.35   $14.40  
  Purchase #6 $112.55   3.410%   $116.388   $116.39   $116.40   $116.40  
  Purchase #7 $24.48   13.278%   $27.7305   $27.73   $27.75   $27.70  
  7 purchase totals = $941.37       $1,014.4987   $1,014.50   $1,014.55   $1,014.50