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 $43.55   3.202%   $44.9445   $44.94   $44.95   $44.90  
  Purchase #2 $203.45   9.452%   $222.6801   $222.68   $222.70   $222.70  
  Purchase #3 $74.83   6.634%   $79.7942   $79.79   $79.80   $79.80  
  Purchase #4 $249.69   10.324%   $275.468   $275.47   $275.45   $275.50  
  Purchase #5 $33.47   7.844%   $36.0954   $36.10   $36.10   $36.10  
  Purchase #6 $99.58   12.618%   $112.145   $112.15   $112.15   $112.10  
  Purchase #7 $152.70   6.449%   $162.5476   $162.55   $162.55   $162.50  
  7 purchase totals = $857.27       $933.6748   $933.68   $933.70   $933.60