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 $68.41   5.146%   $71.9304   $71.93   $71.95   $71.90  
  Purchase #2 $219.56   11.675%   $245.1936   $245.19   $245.20   $245.20  
  Purchase #3 $246.95   12.715%   $278.3497   $278.35   $278.35   $278.30  
  Purchase #4 $131.78   6.616%   $140.4986   $140.50   $140.50   $140.50  
  Purchase #5 $126.38   6.412%   $134.4835   $134.48   $134.50   $134.50  
  Purchase #6 $73.93   8.343%   $80.098   $80.10   $80.10   $80.10  
  Purchase #7 $160.27   13.344%   $181.6564   $181.66   $181.65   $181.70  
  7 purchase totals = $1,027.28       $1,132.2102   $1,132.21   $1,132.25   $1,132.20