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 $32.93   11.343%   $36.6652   $36.67   $36.65   $36.70  
  Purchase #2 $225.74   13.834%   $256.9689   $256.97   $256.95   $257.00  
  Purchase #3 $184.33   12.781%   $207.8892   $207.89   $207.90   $207.90  
  Purchase #4 $166.57   3.248%   $171.9802   $171.98   $172.00   $172.00  
  Purchase #5 $44.33   10.786%   $49.1114   $49.11   $49.10   $49.10  
  Purchase #6 $189.44   3.606%   $196.2712   $196.27   $196.25   $196.30  
  Purchase #7 $119.89   8.467%   $130.0411   $130.04   $130.05   $130.00  
  7 purchase totals = $963.23       $1,048.9272   $1,048.93   $1,048.90   $1,049.00