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 $115.89   11.127%   $128.7851   $128.79   $128.80   $128.80  
  Purchase #2 $100.74   11.825%   $112.6525   $112.65   $112.65   $112.70  
  Purchase #3 $162.58   11.250%   $180.8703   $180.87   $180.85   $180.90  
  Purchase #4 $56.33   8.843%   $61.3113   $61.31   $61.30   $61.30  
  Purchase #5 $115.82   8.297%   $125.4296   $125.43   $125.45   $125.40  
  Purchase #6 $233.37   6.537%   $248.6254   $248.63   $248.65   $248.60  
  Purchase #7 $195.46   8.493%   $212.0604   $212.06   $212.05   $212.10  
  7 purchase totals = $980.19       $1,069.7346   $1,069.74   $1,069.75   $1,069.80