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 $71.81   10.208%   $79.1404   $79.14   $79.15   $79.10  
  Purchase #2 $147.33   8.682%   $160.1212   $160.12   $160.10   $160.10  
  Purchase #3 $239.82   12.452%   $269.6824   $269.68   $269.70   $269.70  
  Purchase #4 $36.57   13.543%   $41.5227   $41.52   $41.50   $41.50  
  Purchase #5 $134.56   4.231%   $140.2532   $140.25   $140.25   $140.30  
  Purchase #6 $8.32   6.190%   $8.835   $8.84   $8.85   $8.80  
  Purchase #7 $112.40   12.846%   $126.8389   $126.84   $126.85   $126.80  
  7 purchase totals = $750.81       $826.3938   $826.39   $826.40   $826.30