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 $184.39   10.594%   $203.9243   $203.92   $203.90   $203.90  
  Purchase #2 $14.41   8.618%   $15.6519   $15.65   $15.65   $15.70  
  Purchase #3 $107.47   5.568%   $113.4539   $113.45   $113.45   $113.50  
  Purchase #4 $219.98   5.319%   $231.6807   $231.68   $231.70   $231.70  
  Purchase #5 $31.91   10.631%   $35.3024   $35.30   $35.30   $35.30  
  Purchase #6 $190.49   3.227%   $196.6371   $196.64   $196.65   $196.60  
  Purchase #7 $108.32   11.480%   $120.7551   $120.76   $120.75   $120.80  
  7 purchase totals = $856.97       $917.4054   $917.40   $917.40   $917.50