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 $203.93   11.322%   $227.019   $227.02   $227.00   $227.00  
  Purchase #2 $227.34   12.201%   $255.0778   $255.08   $255.10   $255.10  
  Purchase #3 $17.49   7.781%   $18.8509   $18.85   $18.85   $18.90  
  Purchase #4 $46.85   12.247%   $52.5877   $52.59   $52.60   $52.60  
  Purchase #5 $35.44   7.770%   $38.1937   $38.19   $38.20   $38.20  
  Purchase #6 $114.44   7.527%   $123.0539   $123.05   $123.05   $123.10  
  Purchase #7 $121.90   9.148%   $133.0514   $133.05   $133.05   $133.10  
  7 purchase totals = $767.39       $847.8344   $847.83   $847.85   $848.00