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 $56.82   6.682%   $60.6167   $60.62   $60.60   $60.60  
  Purchase #2 $79.69   10.810%   $88.3045   $88.30   $88.30   $88.30  
  Purchase #3 $79.80   12.354%   $89.6585   $89.66   $89.65   $89.70  
  Purchase #4 $219.40   8.540%   $238.1368   $238.14   $238.15   $238.10  
  Purchase #5 $141.95   9.332%   $155.1968   $155.20   $155.20   $155.20  
  Purchase #6 $241.25   8.695%   $262.2267   $262.23   $262.25   $262.20  
  Purchase #7 $130.66   7.518%   $140.483   $140.48   $140.50   $140.50  
  7 purchase totals = $949.57       $1,034.6230   $1,034.63   $1,034.65   $1,034.60