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 $147.98   13.638%   $168.1615   $168.16   $168.15   $168.20  
  Purchase #2 $246.40   9.727%   $270.3673   $270.37   $270.35   $270.40  
  Purchase #3 $41.76   13.823%   $47.5325   $47.53   $47.55   $47.50  
  Purchase #4 $225.53   11.799%   $252.1403   $252.14   $252.15   $252.10  
  Purchase #5 $101.74   10.744%   $112.6709   $112.67   $112.65   $112.70  
  Purchase #6 $133.94   9.442%   $146.5866   $146.59   $146.60   $146.60  
  Purchase #7 $21.68   11.246%   $24.1181   $24.12   $24.10   $24.10  
  7 purchase totals = $919.03       $1,021.5772   $1,021.58   $1,021.55   $1,021.60