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 $118.59   7.173%   $127.0965   $127.10   $127.10   $127.10  
  Purchase #2 $23.70   10.673%   $26.2295   $26.23   $26.25   $26.20  
  Purchase #3 $74.52   12.821%   $84.0742   $84.07   $84.05   $84.10  
  Purchase #4 $191.99   6.819%   $205.0818   $205.08   $205.10   $205.10  
  Purchase #5 $208.80   5.717%   $220.7371   $220.74   $220.75   $220.70  
  Purchase #6 $24.63   5.325%   $25.9415   $25.94   $25.95   $25.90  
  Purchase #7 $242.54   10.773%   $268.6688   $268.67   $268.65   $268.70  
  7 purchase totals = $884.77       $957.8294   $957.83   $957.85   $957.80