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 $201.39   12.482%   $226.5275   $226.53   $226.55   $226.50  
  Purchase #2 $209.93   8.603%   $227.9903   $227.99   $228.00   $228.00  
  Purchase #3 $62.93   10.764%   $69.7038   $69.70   $69.70   $69.70  
  Purchase #4 $162.82   5.532%   $171.8272   $171.83   $171.85   $171.80  
  Purchase #5 $124.65   13.213%   $141.12   $141.12   $141.10   $141.10  
  Purchase #6 $121.81   12.782%   $137.3798   $137.38   $137.40   $137.40  
  Purchase #7 $246.70   9.777%   $270.8199   $270.82   $270.80   $270.80  
  7 purchase totals = $1,130.23       $1,245.3685   $1,245.37   $1,245.40   $1,245.30