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 $193.43   13.133%   $218.8332   $218.83   $218.85   $218.80  
  Purchase #2 $237.66   3.655%   $246.3465   $246.35   $246.35   $246.30  
  Purchase #3 $40.55   13.821%   $46.1544   $46.15   $46.15   $46.20  
  Purchase #4 $17.52   10.505%   $19.3605   $19.36   $19.35   $19.40  
  Purchase #5 $173.63   3.394%   $179.523   $179.52   $179.50   $179.50  
  Purchase #6 $219.47   8.157%   $237.3722   $237.37   $237.35   $237.40  
  Purchase #7 $145.85   8.871%   $158.7884   $158.79   $158.80   $158.80  
  7 purchase totals = $1,028.11       $1,106.3782   $1,106.37   $1,106.35   $1,106.40