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 $31.33   11.841%   $35.0398   $35.04   $35.05   $35.00  
  Purchase #2 $124.96   3.847%   $129.7672   $129.77   $129.75   $129.80  
  Purchase #3 $111.48   7.152%   $119.453   $119.45   $119.45   $119.50  
  Purchase #4 $99.91   3.420%   $103.3269   $103.33   $103.35   $103.30  
  Purchase #5 $144.31   13.314%   $163.5234   $163.52   $163.50   $163.50  
  Purchase #6 $173.38   4.560%   $181.2861   $181.29   $181.30   $181.30  
  Purchase #7 $197.84   5.262%   $208.2503   $208.25   $208.25   $208.30  
  7 purchase totals = $883.21       $940.6467   $940.65   $940.65   $940.70