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 $113.42   5.380%   $119.522   $119.52   $119.50   $119.50  
  Purchase #2 $165.66   9.451%   $181.3165   $181.32   $181.30   $181.30  
  Purchase #3 $158.30   11.736%   $176.8781   $176.88   $176.90   $176.90  
  Purchase #4 $42.99   10.282%   $47.4102   $47.41   $47.40   $47.40  
  Purchase #5 $245.75   5.865%   $260.1632   $260.16   $260.15   $260.20  
  Purchase #6 $93.27   11.835%   $104.3085   $104.31   $104.30   $104.30  
  Purchase #7 $140.66   9.150%   $153.5304   $153.53   $153.55   $153.50  
  7 purchase totals = $960.05       $1,043.1289   $1,043.13   $1,043.10   $1,043.10