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 $85.64   3.405%   $88.556   $88.56   $88.55   $88.60  
  Purchase #2 $245.76   3.276%   $253.8111   $253.81   $253.80   $253.80  
  Purchase #3 $230.66   3.851%   $239.5427   $239.54   $239.55   $239.50  
  Purchase #4 $52.56   4.438%   $54.8926   $54.89   $54.90   $54.90  
  Purchase #5 $112.29   4.784%   $117.662   $117.66   $117.65   $117.70  
  Purchase #6 $167.97   8.801%   $182.753   $182.75   $182.75   $182.80  
  Purchase #7 $170.80   12.712%   $192.5121   $192.51   $192.50   $192.50  
  7 purchase totals = $1,065.68       $1,129.7295   $1,129.72   $1,129.70   $1,129.80