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 $205.37   13.345%   $232.7766   $232.78   $232.80   $232.80  
  Purchase #2 $41.36   12.414%   $46.4944   $46.49   $46.50   $46.50  
  Purchase #3 $85.96   8.604%   $93.356   $93.36   $93.35   $93.40  
  Purchase #4 $111.69   6.598%   $119.0593   $119.06   $119.05   $119.10  
  Purchase #5 $112.27   10.332%   $123.8697   $123.87   $123.85   $123.90  
  Purchase #6 $144.67   11.683%   $161.5718   $161.57   $161.55   $161.60  
  Purchase #7 $250.33   11.672%   $279.5485   $279.55   $279.55   $279.50  
  7 purchase totals = $951.65       $1,056.6763   $1,056.68   $1,056.65   $1,056.80