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 $182.55   6.452%   $194.3281   $194.33   $194.35   $194.30  
  Purchase #2 $238.44   12.662%   $268.6313   $268.63   $268.65   $268.60  
  Purchase #3 $231.32   8.175%   $250.2304   $250.23   $250.25   $250.20  
  Purchase #4 $137.38   10.808%   $152.228   $152.23   $152.25   $152.20  
  Purchase #5 $179.84   12.693%   $202.6671   $202.67   $202.65   $202.70  
  Purchase #6 $172.39   11.133%   $191.5822   $191.58   $191.60   $191.60  
  Purchase #7 $170.77   11.576%   $190.5383   $190.54   $190.55   $190.50  
  7 purchase totals = $1,312.69       $1,450.2054   $1,450.21   $1,450.30   $1,450.10