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 $161.62   12.458%   $181.7546   $181.75   $181.75   $181.80  
  Purchase #2 $170.82   4.771%   $178.9698   $178.97   $178.95   $179.00  
  Purchase #3 $186.68   3.177%   $192.6108   $192.61   $192.60   $192.60  
  Purchase #4 $217.56   3.650%   $225.5009   $225.50   $225.50   $225.50  
  Purchase #5 $68.66   7.283%   $73.6605   $73.66   $73.65   $73.70  
  Purchase #6 $132.67   11.584%   $148.0385   $148.04   $148.05   $148.00  
  Purchase #7 $238.61   13.644%   $271.1659   $271.17   $271.15   $271.20  
  7 purchase totals = $1,176.62       $1,271.7010   $1,271.70   $1,271.65   $1,271.80