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 $23.93   10.848%   $26.5259   $26.53   $26.55   $26.50  
  Purchase #2 $137.45   12.668%   $154.8622   $154.86   $154.85   $154.90  
  Purchase #3 $99.29   5.287%   $104.5395   $104.54   $104.55   $104.50  
  Purchase #4 $203.47   11.719%   $227.3146   $227.31   $227.30   $227.30  
  Purchase #5 $24.96   13.644%   $28.3655   $28.37   $28.35   $28.40  
  Purchase #6 $244.34   10.692%   $270.4648   $270.46   $270.45   $270.50  
  Purchase #7 $215.44   11.170%   $239.5046   $239.50   $239.50   $239.50  
  7 purchase totals = $948.88       $1,051.5771   $1,051.57   $1,051.55   $1,051.60