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 $167.30   11.614%   $186.7302   $186.73   $186.75   $186.70  
  Purchase #2 $161.91   6.823%   $172.9571   $172.96   $172.95   $173.00  
  Purchase #3 $54.99   11.135%   $61.1131   $61.11   $61.10   $61.10  
  Purchase #4 $231.57   8.275%   $250.7324   $250.73   $250.75   $250.70  
  Purchase #5 $217.41   10.644%   $240.5511   $240.55   $240.55   $240.60  
  Purchase #6 $236.56   13.525%   $268.5547   $268.55   $268.55   $268.60  
  Purchase #7 $203.81   9.601%   $223.3778   $223.38   $223.40   $223.40  
  7 purchase totals = $1,273.55       $1,404.0164   $1,404.01   $1,404.05   $1,404.10