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 $138.74   9.567%   $152.0133   $152.01   $152.00   $152.00  
  Purchase #2 $76.53   13.602%   $86.9396   $86.94   $86.95   $86.90  
  Purchase #3 $213.66   9.317%   $233.5667   $233.57   $233.55   $233.60  
  Purchase #4 $53.53   6.568%   $57.0459   $57.05   $57.05   $57.00  
  Purchase #5 $219.78   11.487%   $245.0261   $245.03   $245.05   $245.00  
  Purchase #6 $219.72   7.399%   $235.9771   $235.98   $236.00   $236.00  
  Purchase #7 $60.99   4.718%   $63.8675   $63.87   $63.85   $63.90  
  7 purchase totals = $982.95       $1,074.4362   $1,074.45   $1,074.45   $1,074.40