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 $161.58   13.719%   $183.7472   $183.75   $183.75   $183.70  
  Purchase #2 $49.51   4.133%   $51.5562   $51.56   $51.55   $51.60  
  Purchase #3 $170.31   10.862%   $188.8091   $188.81   $188.80   $188.80  
  Purchase #4 $219.91   11.221%   $244.5861   $244.59   $244.60   $244.60  
  Purchase #5 $214.31   11.296%   $238.5185   $238.52   $238.50   $238.50  
  Purchase #6 $218.97   3.781%   $227.2493   $227.25   $227.25   $227.20  
  Purchase #7 $110.94   9.262%   $121.2153   $121.22   $121.20   $121.20  
  7 purchase totals = $1,145.53       $1,255.6817   $1,255.70   $1,255.65   $1,255.60