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 $7.81   5.578%   $8.2456   $8.25   $8.25   $8.20  
  Purchase #2 $112.28   11.873%   $125.611   $125.61   $125.60   $125.60  
  Purchase #3 $171.71   5.734%   $181.5559   $181.56   $181.55   $181.60  
  Purchase #4 $95.76   8.518%   $103.9168   $103.92   $103.90   $103.90  
  Purchase #5 $93.59   11.110%   $103.9878   $103.99   $104.00   $104.00  
  Purchase #6 $122.62   6.481%   $130.567   $130.57   $130.55   $130.60  
  Purchase #7 $196.42   5.191%   $206.6162   $206.62   $206.60   $206.60  
  7 purchase totals = $800.19       $860.5003   $860.52   $860.45   $860.50