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 $30.92   7.141%   $33.128   $33.13   $33.15   $33.10  
  Purchase #2 $171.47   6.302%   $182.276   $182.28   $182.30   $182.30  
  Purchase #3 $227.52   4.124%   $236.9029   $236.90   $236.90   $236.90  
  Purchase #4 $239.86   11.764%   $268.0771   $268.08   $268.10   $268.10  
  Purchase #5 $136.54   10.656%   $151.0897   $151.09   $151.10   $151.10  
  Purchase #6 $162.29   7.826%   $174.9908   $174.99   $175.00   $175.00  
  Purchase #7 $230.57   10.689%   $255.2156   $255.22   $255.20   $255.20  
  7 purchase totals = $1,199.17       $1,301.6801   $1,301.69   $1,301.75   $1,301.70