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 $6.50   11.476%   $7.2459   $7.25   $7.25   $7.20  
  Purchase #2 $145.97   12.687%   $164.4892   $164.49   $164.50   $164.50  
  Purchase #3 $168.57   11.503%   $187.9606   $187.96   $187.95   $188.00  
  Purchase #4 $248.48   9.705%   $272.595   $272.60   $272.60   $272.60  
  Purchase #5 $112.71   3.596%   $116.7631   $116.76   $116.75   $116.80  
  Purchase #6 $232.73   5.692%   $245.977   $245.98   $246.00   $246.00  
  Purchase #7 $175.59   3.359%   $181.4881   $181.49   $181.50   $181.50  
  7 purchase totals = $1,090.55       $1,176.5189   $1,176.53   $1,176.55   $1,176.60