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 $120.61   11.282%   $134.2172   $134.22   $134.20   $134.20  
  Purchase #2 $141.61   4.230%   $147.6001   $147.60   $147.60   $147.60  
  Purchase #3 $52.61   4.575%   $55.0169   $55.02   $55.00   $55.00  
  Purchase #4 $187.87   13.202%   $212.6726   $212.67   $212.65   $212.70  
  Purchase #5 $207.65   12.536%   $233.681   $233.68   $233.70   $233.70  
  Purchase #6 $180.53   4.620%   $188.8705   $188.87   $188.85   $188.90  
  Purchase #7 $34.81   6.351%   $37.0208   $37.02   $37.00   $37.00  
  7 purchase totals = $925.69       $1,009.0791   $1,009.08   $1,009.00   $1,009.10