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 $182.30   12.268%   $204.6646   $204.66   $204.65   $204.70  
  Purchase #2 $201.53   12.444%   $226.6084   $226.61   $226.60   $226.60  
  Purchase #3 $76.37   8.444%   $82.8187   $82.82   $82.80   $82.80  
  Purchase #4 $219.84   11.669%   $245.4931   $245.49   $245.50   $245.50  
  Purchase #5 $234.95   4.140%   $244.6769   $244.68   $244.70   $244.70  
  Purchase #6 $30.97   11.259%   $34.4569   $34.46   $34.45   $34.50  
  Purchase #7 $40.84   12.874%   $46.0977   $46.10   $46.10   $46.10  
  7 purchase totals = $986.80       $1,084.8163   $1,084.82   $1,084.80   $1,084.90