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 $231.74   13.338%   $262.6495   $262.65   $262.65   $262.60  
  Purchase #2 $62.33   10.117%   $68.6359   $68.64   $68.65   $68.60  
  Purchase #3 $216.84   11.637%   $242.0737   $242.07   $242.05   $242.10  
  Purchase #4 $219.79   10.265%   $242.3514   $242.35   $242.35   $242.40  
  Purchase #5 $68.79   9.519%   $75.3381   $75.34   $75.35   $75.30  
  Purchase #6 $62.26   8.846%   $67.7675   $67.77   $67.75   $67.80  
  Purchase #7 $114.70   6.838%   $122.5432   $122.54   $122.55   $122.50  
  7 purchase totals = $976.45       $1,081.3593   $1,081.36   $1,081.35   $1,081.30