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 $146.82   10.202%   $161.7986   $161.80   $161.80   $161.80  
  Purchase #2 $208.68   7.163%   $223.6277   $223.63   $223.65   $223.60  
  Purchase #3 $115.85   5.847%   $122.6237   $122.62   $122.60   $122.60  
  Purchase #4 $216.68   5.324%   $228.216   $228.22   $228.20   $228.20  
  Purchase #5 $244.37   3.337%   $252.5246   $252.52   $252.50   $252.50  
  Purchase #6 $208.47   10.537%   $230.4365   $230.44   $230.45   $230.40  
  Purchase #7 $186.70   7.724%   $201.1207   $201.12   $201.10   $201.10  
  7 purchase totals = $1,327.57       $1,420.3478   $1,420.35   $1,420.30   $1,420.20