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 $97.79   3.561%   $101.2723   $101.27   $101.25   $101.30  
  Purchase #2 $29.93   10.559%   $33.0903   $33.09   $33.10   $33.10  
  Purchase #3 $82.88   11.293%   $92.2396   $92.24   $92.25   $92.20  
  Purchase #4 $90.43   10.197%   $99.6511   $99.65   $99.65   $99.70  
  Purchase #5 $157.78   9.512%   $172.788   $172.79   $172.80   $172.80  
  Purchase #6 $184.48   11.582%   $205.8465   $205.85   $205.85   $205.80  
  Purchase #7 $163.79   8.850%   $178.2854   $178.29   $178.30   $178.30  
  7 purchase totals = $807.08       $883.1732   $883.18   $883.20   $883.20