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 $52.45   6.209%   $55.7066   $55.71   $55.70   $55.70  
  Purchase #2 $218.93   9.245%   $239.1701   $239.17   $239.15   $239.20  
  Purchase #3 $215.75   8.849%   $234.8417   $234.84   $234.85   $234.80  
  Purchase #4 $232.72   9.823%   $255.5801   $255.58   $255.60   $255.60  
  Purchase #5 $61.89   3.663%   $64.157   $64.16   $64.15   $64.20  
  Purchase #6 $112.56   7.518%   $121.0223   $121.02   $121.00   $121.00  
  Purchase #7 $56.28   12.344%   $63.2272   $63.23   $63.25   $63.20  
  7 purchase totals = $950.58       $1,033.7050   $1,033.71   $1,033.70   $1,033.70