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 $73.55   13.783%   $83.6874   $83.69   $83.70   $83.70  
  Purchase #2 $235.76   10.133%   $259.6496   $259.65   $259.65   $259.60  
  Purchase #3 $16.73   8.524%   $18.1561   $18.16   $18.15   $18.20  
  Purchase #4 $187.26   11.654%   $209.0833   $209.08   $209.10   $209.10  
  Purchase #5 $205.39   12.665%   $231.4026   $231.40   $231.40   $231.40  
  Purchase #6 $182.26   4.171%   $189.8621   $189.86   $189.85   $189.90  
  Purchase #7 $164.91   3.340%   $170.418   $170.42   $170.40   $170.40  
  7 purchase totals = $1,065.86       $1,162.2591   $1,162.26   $1,162.25   $1,162.30