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 $92.68   11.611%   $103.4411   $103.44   $103.45   $103.40  
  Purchase #2 $195.88   3.304%   $202.3519   $202.35   $202.35   $202.40  
  Purchase #3 $117.76   10.380%   $129.9835   $129.98   $130.00   $130.00  
  Purchase #4 $142.66   3.293%   $147.3578   $147.36   $147.35   $147.40  
  Purchase #5 $231.41   12.180%   $259.5957   $259.60   $259.60   $259.60  
  Purchase #6 $23.26   6.683%   $24.8145   $24.81   $24.80   $24.80  
  Purchase #7 $175.94   10.275%   $194.0178   $194.02   $194.00   $194.00  
  7 purchase totals = $979.59       $1,061.5623   $1,061.56   $1,061.55   $1,061.60