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 $49.60   10.141%   $54.6299   $54.63   $54.65   $54.60  
  Purchase #2 $208.74   7.827%   $225.0781   $225.08   $225.10   $225.10  
  Purchase #3 $179.72   3.731%   $186.4254   $186.43   $186.45   $186.40  
  Purchase #4 $59.86   3.841%   $62.1592   $62.16   $62.15   $62.20  
  Purchase #5 $111.65   5.433%   $117.7159   $117.72   $117.70   $117.70  
  Purchase #6 $38.79   13.429%   $43.9991   $44.00   $44.00   $44.00  
  Purchase #7 $146.77   8.156%   $158.7406   $158.74   $158.75   $158.70  
  7 purchase totals = $795.13       $848.7482   $848.76   $848.80   $848.70