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 $120.54   9.701%   $132.2336   $132.23   $132.25   $132.20  
  Purchase #2 $223.39   9.866%   $245.4297   $245.43   $245.45   $245.40  
  Purchase #3 $171.65   4.695%   $179.709   $179.71   $179.70   $179.70  
  Purchase #4 $27.65   6.138%   $29.3472   $29.35   $29.35   $29.30  
  Purchase #5 $180.43   4.641%   $188.8038   $188.80   $188.80   $188.80  
  Purchase #6 $49.74   5.722%   $52.5861   $52.59   $52.60   $52.60  
  Purchase #7 $203.99   5.639%   $215.493   $215.49   $215.50   $215.50  
  7 purchase totals = $977.39       $1,043.6024   $1,043.60   $1,043.65   $1,043.50