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 $168.46   9.634%   $184.6894   $184.69   $184.70   $184.70  
  Purchase #2 $63.74   6.121%   $67.6415   $67.64   $67.65   $67.60  
  Purchase #3 $64.75   9.138%   $70.6669   $70.67   $70.65   $70.70  
  Purchase #4 $243.54   4.429%   $254.3264   $254.33   $254.35   $254.30  
  Purchase #5 $38.38   4.284%   $40.0242   $40.02   $40.00   $40.00  
  Purchase #6 $23.53   7.715%   $25.3453   $25.35   $25.35   $25.30  
  Purchase #7 $201.25   10.581%   $222.5443   $222.54   $222.55   $222.50  
  7 purchase totals = $803.65       $865.2380   $865.24   $865.25   $865.10