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 $63.42   5.373%   $66.8276   $66.83   $66.85   $66.80  
  Purchase #2 $26.92   6.816%   $28.7549   $28.75   $28.75   $28.80  
  Purchase #3 $181.58   13.457%   $206.0152   $206.02   $206.00   $206.00  
  Purchase #4 $113.71   10.189%   $125.2959   $125.30   $125.30   $125.30  
  Purchase #5 $112.82   12.839%   $127.305   $127.31   $127.30   $127.30  
  Purchase #6 $236.90   9.613%   $259.6732   $259.67   $259.65   $259.70  
  Purchase #7 $181.87   10.872%   $201.6429   $201.64   $201.65   $201.60  
  7 purchase totals = $917.22       $1,015.5147   $1,015.52   $1,015.50   $1,015.50