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 $153.69   9.312%   $168.0016   $168.00   $168.00   $168.00  
  Purchase #2 $18.69   6.210%   $19.8506   $19.85   $19.85   $19.90  
  Purchase #3 $44.45   7.226%   $47.662   $47.66   $47.65   $47.70  
  Purchase #4 $184.57   9.257%   $201.6556   $201.66   $201.65   $201.70  
  Purchase #5 $214.35   13.626%   $243.5573   $243.56   $243.55   $243.60  
  Purchase #6 $148.42   10.806%   $164.4583   $164.46   $164.45   $164.50  
  Purchase #7 $208.40   13.495%   $236.5236   $236.52   $236.50   $236.50  
  7 purchase totals = $972.57       $1,081.7090   $1,081.71   $1,081.65   $1,081.90