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 $214.90   13.467%   $243.8406   $243.84   $243.85   $243.80  
  Purchase #2 $182.74   5.349%   $192.5148   $192.51   $192.50   $192.50  
  Purchase #3 $77.58   6.337%   $82.4962   $82.50   $82.50   $82.50  
  Purchase #4 $8.90   4.808%   $9.3279   $9.33   $9.35   $9.30  
  Purchase #5 $140.89   4.754%   $147.5879   $147.59   $147.60   $147.60  
  Purchase #6 $200.49   12.608%   $225.7678   $225.77   $225.75   $225.80  
  Purchase #7 $89.55   6.527%   $95.3949   $95.39   $95.40   $95.40  
  7 purchase totals = $915.05       $996.9301   $996.93   $996.95   $996.90