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 $218.33   12.657%   $245.964   $245.96   $245.95   $246.00  
  Purchase #2 $230.87   10.353%   $254.772   $254.77   $254.75   $254.80  
  Purchase #3 $139.64   4.141%   $145.4225   $145.42   $145.40   $145.40  
  Purchase #4 $80.43   12.349%   $90.3623   $90.36   $90.35   $90.40  
  Purchase #5 $178.64   10.320%   $197.0756   $197.08   $197.10   $197.10  
  Purchase #6 $245.90   4.795%   $257.6909   $257.69   $257.70   $257.70  
  Purchase #7 $157.42   9.266%   $172.0065   $172.01   $172.00   $172.00  
  7 purchase totals = $1,251.23       $1,363.2938   $1,363.29   $1,363.25   $1,363.40