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 $202.96   5.604%   $214.3339   $214.33   $214.35   $214.30  
  Purchase #2 $180.35   6.784%   $192.5849   $192.58   $192.60   $192.60  
  Purchase #3 $211.94   11.804%   $236.9574   $236.96   $236.95   $237.00  
  Purchase #4 $214.70   7.203%   $230.1648   $230.16   $230.15   $230.20  
  Purchase #5 $23.75   10.551%   $26.2559   $26.26   $26.25   $26.30  
  Purchase #6 $183.27   12.700%   $206.5453   $206.55   $206.55   $206.50  
  Purchase #7 $86.75   8.873%   $94.4473   $94.45   $94.45   $94.40  
  7 purchase totals = $1,103.72       $1,201.2895   $1,201.29   $1,201.30   $1,201.30