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 $168.96   3.301%   $174.5374   $174.54   $174.55   $174.50  
  Purchase #2 $247.89   10.433%   $273.7524   $273.75   $273.75   $273.80  
  Purchase #3 $92.30   9.491%   $101.0602   $101.06   $101.05   $101.10  
  Purchase #4 $240.98   12.814%   $271.8592   $271.86   $271.85   $271.90  
  Purchase #5 $240.63   12.838%   $271.5221   $271.52   $271.50   $271.50  
  Purchase #6 $162.51   13.348%   $184.2018   $184.20   $184.20   $184.20  
  Purchase #7 $32.31   4.262%   $33.6871   $33.69   $33.70   $33.70  
  7 purchase totals = $1,185.58       $1,310.6202   $1,310.62   $1,310.60   $1,310.70