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 $214.71   13.816%   $244.3743   $244.37   $244.35   $244.40  
  Purchase #2 $156.49   6.414%   $166.5273   $166.53   $166.55   $166.50  
  Purchase #3 $40.76   6.285%   $43.3218   $43.32   $43.30   $43.30  
  Purchase #4 $207.93   12.650%   $234.2331   $234.23   $234.25   $234.20  
  Purchase #5 $134.42   11.277%   $149.5785   $149.58   $149.60   $149.60  
  Purchase #6 $24.62   13.760%   $28.0077   $28.01   $28.00   $28.00  
  Purchase #7 $233.96   4.163%   $243.6998   $243.70   $243.70   $243.70  
  7 purchase totals = $1,012.89       $1,109.7425   $1,109.74   $1,109.75   $1,109.70