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 $236.43   13.151%   $267.5229   $267.52   $267.50   $267.50  
  Purchase #2 $149.39   11.557%   $166.655   $166.66   $166.65   $166.70  
  Purchase #3 $35.90   3.427%   $37.1303   $37.13   $37.15   $37.10  
  Purchase #4 $232.65   6.463%   $247.6862   $247.69   $247.70   $247.70  
  Purchase #5 $11.52   13.330%   $13.0556   $13.06   $13.05   $13.10  
  Purchase #6 $206.40   5.607%   $217.9728   $217.97   $217.95   $218.00  
  Purchase #7 $171.57   11.691%   $191.6282   $191.63   $191.65   $191.60  
  7 purchase totals = $1,043.86       $1,141.6510   $1,141.66   $1,141.65   $1,141.70