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 $32.89   3.267%   $33.9645   $33.96   $33.95   $34.00  
  Purchase #2 $244.53   5.482%   $257.9351   $257.94   $257.95   $257.90  
  Purchase #3 $76.33   5.796%   $80.7541   $80.75   $80.75   $80.80  
  Purchase #4 $221.66   5.243%   $233.2816   $233.28   $233.30   $233.30  
  Purchase #5 $152.48   6.661%   $162.6367   $162.64   $162.65   $162.60  
  Purchase #6 $116.58   10.501%   $128.8221   $128.82   $128.80   $128.80  
  Purchase #7 $250.61   11.229%   $278.751   $278.75   $278.75   $278.80  
  7 purchase totals = $1,095.08       $1,176.1451   $1,176.14   $1,176.15   $1,176.20