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 $56.62   3.267%   $58.4698   $58.47   $58.45   $58.50  
  Purchase #2 $195.51   4.151%   $203.6256   $203.63   $203.65   $203.60  
  Purchase #3 $16.40   10.846%   $18.1787   $18.18   $18.20   $18.20  
  Purchase #4 $196.39   5.851%   $207.8808   $207.88   $207.90   $207.90  
  Purchase #5 $153.56   8.165%   $166.0982   $166.10   $166.10   $166.10  
  Purchase #6 $147.96   12.849%   $166.9714   $166.97   $166.95   $167.00  
  Purchase #7 $21.85   12.855%   $24.6588   $24.66   $24.65   $24.70  
  7 purchase totals = $788.29       $845.8833   $845.89   $845.90   $846.00