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 $50.41   6.360%   $53.6161   $53.62   $53.60   $53.60  
  Purchase #2 $91.68   12.724%   $103.3454   $103.35   $103.35   $103.30  
  Purchase #3 $234.43   12.783%   $264.3972   $264.40   $264.40   $264.40  
  Purchase #4 $245.50   13.530%   $278.7162   $278.72   $278.70   $278.70  
  Purchase #5 $127.50   3.294%   $131.6999   $131.70   $131.70   $131.70  
  Purchase #6 $231.40   6.794%   $247.1213   $247.12   $247.10   $247.10  
  Purchase #7 $247.91   9.866%   $272.3688   $272.37   $272.35   $272.40  
  7 purchase totals = $1,228.83       $1,351.2649   $1,351.28   $1,351.20   $1,351.20