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 $219.41   11.826%   $245.3574   $245.36   $245.35   $245.40  
  Purchase #2 $153.47   9.479%   $168.0174   $168.02   $168.00   $168.00  
  Purchase #3 $60.50   4.736%   $63.3653   $63.37   $63.35   $63.40  
  Purchase #4 $93.54   9.338%   $102.2748   $102.27   $102.25   $102.30  
  Purchase #5 $116.86   6.419%   $124.3612   $124.36   $124.35   $124.40  
  Purchase #6 $132.95   4.593%   $139.0564   $139.06   $139.05   $139.10  
  Purchase #7 $203.77   7.872%   $219.8108   $219.81   $219.80   $219.80  
  7 purchase totals = $980.50       $1,062.2433   $1,062.25   $1,062.15   $1,062.40