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 $232.92   13.196%   $263.6561   $263.66   $263.65   $263.70  
  Purchase #2 $185.40   4.405%   $193.5669   $193.57   $193.55   $193.60  
  Purchase #3 $159.28   8.537%   $172.8777   $172.88   $172.90   $172.90  
  Purchase #4 $195.54   8.790%   $212.728   $212.73   $212.75   $212.70  
  Purchase #5 $226.51   12.533%   $254.8985   $254.90   $254.90   $254.90  
  Purchase #6 $228.42   5.600%   $241.2115   $241.21   $241.20   $241.20  
  Purchase #7 $202.39   10.423%   $223.4851   $223.49   $223.50   $223.50  
  7 purchase totals = $1,430.46       $1,562.4238   $1,562.44   $1,562.45   $1,562.50