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 $218.86   3.425%   $226.356   $226.36   $226.35   $226.40  
  Purchase #2 $72.56   11.160%   $80.6577   $80.66   $80.65   $80.70  
  Purchase #3 $235.47   4.104%   $245.1337   $245.13   $245.15   $245.10  
  Purchase #4 $24.99   10.727%   $27.6707   $27.67   $27.65   $27.70  
  Purchase #5 $75.74   6.418%   $80.601   $80.60   $80.60   $80.60  
  Purchase #6 $150.65   4.337%   $157.1837   $157.18   $157.20   $157.20  
  Purchase #7 $190.54   8.687%   $207.0922   $207.09   $207.10   $207.10  
  7 purchase totals = $968.81       $1,024.6950   $1,024.69   $1,024.70   $1,024.80