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 $86.46   6.473%   $92.0566   $92.06   $92.05   $92.10  
  Purchase #2 $14.47   11.868%   $16.1873   $16.19   $16.20   $16.20  
  Purchase #3 $242.53   3.687%   $251.4721   $251.47   $251.45   $251.50  
  Purchase #4 $119.88   7.459%   $128.8218   $128.82   $128.80   $128.80  
  Purchase #5 $209.57   6.685%   $223.5798   $223.58   $223.60   $223.60  
  Purchase #6 $149.42   6.520%   $159.1622   $159.16   $159.15   $159.20  
  Purchase #7 $124.72   6.556%   $132.8966   $132.90   $132.90   $132.90  
  7 purchase totals = $947.05       $1,004.1764   $1,004.18   $1,004.15   $1,004.30