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 $182.94   12.734%   $206.2356   $206.24   $206.25   $206.20  
  Purchase #2 $48.85   8.391%   $52.949   $52.95   $52.95   $52.90  
  Purchase #3 $148.89   4.656%   $155.8223   $155.82   $155.80   $155.80  
  Purchase #4 $39.78   4.587%   $41.6047   $41.60   $41.60   $41.60  
  Purchase #5 $112.66   6.783%   $120.3017   $120.30   $120.30   $120.30  
  Purchase #6 $233.89   7.209%   $250.7511   $250.75   $250.75   $250.80  
  Purchase #7 $236.83   6.349%   $251.8663   $251.87   $251.85   $251.90  
  7 purchase totals = $1,003.84       $1,079.5307   $1,079.53   $1,079.50   $1,079.50