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 $113.59   11.157%   $126.2632   $126.26   $126.25   $126.30  
  Purchase #2 $75.39   13.694%   $85.7139   $85.71   $85.70   $85.70  
  Purchase #3 $159.52   11.377%   $177.6686   $177.67   $177.65   $177.70  
  Purchase #4 $127.86   7.581%   $137.5531   $137.55   $137.55   $137.60  
  Purchase #5 $26.75   10.561%   $29.5751   $29.58   $29.60   $29.60  
  Purchase #6 $107.45   4.777%   $112.5829   $112.58   $112.60   $112.60  
  Purchase #7 $246.72   6.708%   $263.27   $263.27   $263.25   $263.30  
  7 purchase totals = $857.28       $932.6268   $932.62   $932.60   $932.80