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 $232.66   11.874%   $260.286   $260.29   $260.30   $260.30  
  Purchase #2 $193.64   7.759%   $208.6645   $208.66   $208.65   $208.70  
  Purchase #3 $39.61   9.490%   $43.369   $43.37   $43.35   $43.40  
  Purchase #4 $138.52   10.672%   $153.3029   $153.30   $153.30   $153.30  
  Purchase #5 $43.44   13.666%   $49.3765   $49.38   $49.40   $49.40  
  Purchase #6 $112.46   8.537%   $122.0607   $122.06   $122.05   $122.10  
  Purchase #7 $195.60   11.668%   $218.4226   $218.42   $218.40   $218.40  
  7 purchase totals = $955.93       $1,055.4822   $1,055.48   $1,055.45   $1,055.60