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 $101.29   10.243%   $111.6651   $111.67   $111.65   $111.70  
  Purchase #2 $187.85   9.140%   $205.0195   $205.02   $205.00   $205.00  
  Purchase #3 $58.71   13.130%   $66.4186   $66.42   $66.40   $66.40  
  Purchase #4 $239.28   7.512%   $257.2547   $257.25   $257.25   $257.30  
  Purchase #5 $129.46   13.729%   $147.2336   $147.23   $147.25   $147.20  
  Purchase #6 $119.33   6.493%   $127.0781   $127.08   $127.10   $127.10  
  Purchase #7 $67.34   5.437%   $71.0013   $71.00   $71.00   $71.00  
  7 purchase totals = $903.26       $985.6709   $985.67   $985.65   $985.70