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 $245.33   12.617%   $276.2833   $276.28   $276.30   $276.30  
  Purchase #2 $230.93   9.829%   $253.6281   $253.63   $253.65   $253.60  
  Purchase #3 $124.84   8.534%   $135.4938   $135.49   $135.50   $135.50  
  Purchase #4 $127.43   8.813%   $138.6604   $138.66   $138.65   $138.70  
  Purchase #5 $178.30   11.775%   $199.2948   $199.29   $199.30   $199.30  
  Purchase #6 $62.64   11.664%   $69.9463   $69.95   $69.95   $69.90  
  Purchase #7 $36.74   12.758%   $41.4273   $41.43   $41.45   $41.40  
  7 purchase totals = $1,006.21       $1,114.7340   $1,114.73   $1,114.80   $1,114.70