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 $160.81   10.217%   $177.24   $177.24   $177.25   $177.20  
  Purchase #2 $218.90   5.804%   $231.605   $231.61   $231.60   $231.60  
  Purchase #3 $239.52   4.815%   $251.0529   $251.05   $251.05   $251.10  
  Purchase #4 $163.90   7.166%   $175.6451   $175.65   $175.65   $175.60  
  Purchase #5 $102.27   5.497%   $107.8918   $107.89   $107.90   $107.90  
  Purchase #6 $111.68   9.135%   $121.882   $121.88   $121.90   $121.90  
  Purchase #7 $137.46   5.672%   $145.2567   $145.26   $145.25   $145.30  
  7 purchase totals = $1,134.54       $1,210.5735   $1,210.58   $1,210.60   $1,210.60