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 $242.97   6.398%   $258.5152   $258.52   $258.50   $258.50  
  Purchase #2 $161.33   5.156%   $169.6482   $169.65   $169.65   $169.60  
  Purchase #3 $8.36   10.613%   $9.2472   $9.25   $9.25   $9.20  
  Purchase #4 $64.69   3.207%   $66.7646   $66.76   $66.75   $66.80  
  Purchase #5 $219.68   7.355%   $235.8375   $235.84   $235.85   $235.80  
  Purchase #6 $225.41   3.617%   $233.5631   $233.56   $233.55   $233.60  
  Purchase #7 $196.30   3.135%   $202.454   $202.45   $202.45   $202.50  
  7 purchase totals = $1,118.74       $1,176.0298   $1,176.03   $1,176.00   $1,176.00