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 $103.66   6.637%   $110.5399   $110.54   $110.55   $110.50  
  Purchase #2 $60.87   11.141%   $67.6515   $67.65   $67.65   $67.70  
  Purchase #3 $58.43   9.197%   $63.8038   $63.80   $63.80   $63.80  
  Purchase #4 $161.69   12.491%   $181.8867   $181.89   $181.90   $181.90  
  Purchase #5 $215.92   8.180%   $233.5823   $233.58   $233.60   $233.60  
  Purchase #6 $151.83   8.798%   $165.188   $165.19   $165.20   $165.20  
  Purchase #7 $193.77   5.447%   $204.3247   $204.32   $204.30   $204.30  
  7 purchase totals = $946.17       $1,026.9769   $1,026.97   $1,027.00   $1,027.00