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 $171.26   6.819%   $182.9382   $182.94   $182.95   $182.90  
  Purchase #2 $219.46   12.147%   $246.1178   $246.12   $246.10   $246.10  
  Purchase #3 $190.85   5.764%   $201.8506   $201.85   $201.85   $201.90  
  Purchase #4 $74.77   13.295%   $84.7107   $84.71   $84.70   $84.70  
  Purchase #5 $5.41   3.732%   $5.6119   $5.61   $5.60   $5.60  
  Purchase #6 $108.97   12.631%   $122.734   $122.73   $122.75   $122.70  
  Purchase #7 $187.41   4.682%   $196.1845   $196.18   $196.20   $196.20  
  7 purchase totals = $958.13       $1,040.1477   $1,040.14   $1,040.15   $1,040.10