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 $110.27   11.399%   $122.8397   $122.84   $122.85   $122.80  
  Purchase #2 $249.43   11.431%   $277.9423   $277.94   $277.95   $277.90  
  Purchase #3 $69.87   4.484%   $73.003   $73.00   $73.00   $73.00  
  Purchase #4 $23.56   11.856%   $26.3533   $26.35   $26.35   $26.40  
  Purchase #5 $230.88   7.837%   $248.9741   $248.97   $248.95   $249.00  
  Purchase #6 $137.63   12.852%   $155.3182   $155.32   $155.30   $155.30  
  Purchase #7 $237.74   5.400%   $250.578   $250.58   $250.60   $250.60  
  7 purchase totals = $1,059.38       $1,155.0086   $1,155.00   $1,155.00   $1,155.00