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 $244.97   9.812%   $269.0065   $269.01   $269.00   $269.00  
  Purchase #2 $62.98   5.748%   $66.6001   $66.60   $66.60   $66.60  
  Purchase #3 $7.40   11.709%   $8.2665   $8.27   $8.25   $8.30  
  Purchase #4 $125.57   13.847%   $142.9577   $142.96   $142.95   $143.00  
  Purchase #5 $139.40   11.619%   $155.5969   $155.60   $155.60   $155.60  
  Purchase #6 $231.80   10.292%   $255.6569   $255.66   $255.65   $255.70  
  Purchase #7 $109.71   13.819%   $124.8708   $124.87   $124.85   $124.90  
  7 purchase totals = $921.83       $1,022.9554   $1,022.97   $1,022.90   $1,023.10