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 $246.29   10.212%   $271.4411   $271.44   $271.45   $271.40  
  Purchase #2 $231.62   8.124%   $250.4368   $250.44   $250.45   $250.40  
  Purchase #3 $13.30   10.602%   $14.7101   $14.71   $14.70   $14.70  
  Purchase #4 $62.40   9.531%   $68.3473   $68.35   $68.35   $68.30  
  Purchase #5 $217.25   9.397%   $237.665   $237.67   $237.65   $237.70  
  Purchase #6 $124.84   10.298%   $137.696   $137.70   $137.70   $137.70  
  Purchase #7 $84.96   12.861%   $95.8867   $95.89   $95.90   $95.90  
  7 purchase totals = $980.66       $1,076.1830   $1,076.20   $1,076.20   $1,076.10