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 $144.84   8.273%   $156.8226   $156.82   $156.80   $156.80  
  Purchase #2 $171.81   7.488%   $184.6751   $184.68   $184.70   $184.70  
  Purchase #3 $68.82   8.622%   $74.7537   $74.75   $74.75   $74.80  
  Purchase #4 $63.74   11.239%   $70.9037   $70.90   $70.90   $70.90  
  Purchase #5 $178.98   10.498%   $197.7693   $197.77   $197.75   $197.80  
  Purchase #6 $212.25   9.498%   $232.4095   $232.41   $232.40   $232.40  
  Purchase #7 $189.65   6.807%   $202.5595   $202.56   $202.55   $202.60  
  7 purchase totals = $1,030.09       $1,119.8934   $1,119.89   $1,119.85   $1,120.00