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 $46.47   6.413%   $49.4501   $49.45   $49.45   $49.50  
  Purchase #2 $93.69   11.352%   $104.3257   $104.33   $104.35   $104.30  
  Purchase #3 $12.49   7.769%   $13.4603   $13.46   $13.45   $13.50  
  Purchase #4 $205.86   7.474%   $221.246   $221.25   $221.25   $221.20  
  Purchase #5 $140.83   9.127%   $153.6836   $153.68   $153.70   $153.70  
  Purchase #6 $218.75   13.495%   $248.2703   $248.27   $248.25   $248.30  
  Purchase #7 $244.94   5.352%   $258.0492   $258.05   $258.05   $258.00  
  7 purchase totals = $963.03       $1,048.4852   $1,048.49   $1,048.50   $1,048.50