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 $139.46   8.773%   $151.6948   $151.69   $151.70   $151.70  
  Purchase #2 $56.88   9.693%   $62.3934   $62.39   $62.40   $62.40  
  Purchase #3 $242.74   3.320%   $250.799   $250.80   $250.80   $250.80  
  Purchase #4 $13.65   4.843%   $14.3111   $14.31   $14.30   $14.30  
  Purchase #5 $210.74   9.505%   $230.7708   $230.77   $230.75   $230.80  
  Purchase #6 $243.86   13.175%   $275.9886   $275.99   $276.00   $276.00  
  Purchase #7 $126.91   5.377%   $133.734   $133.73   $133.75   $133.70  
  7 purchase totals = $1,034.24       $1,119.6917   $1,119.68   $1,119.70   $1,119.70