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 $184.57   12.686%   $207.9846   $207.98   $208.00   $208.00  
  Purchase #2 $22.39   8.812%   $24.363   $24.36   $24.35   $24.40  
  Purchase #3 $25.95   10.848%   $28.7651   $28.77   $28.75   $28.80  
  Purchase #4 $86.35   11.137%   $95.9668   $95.97   $95.95   $96.00  
  Purchase #5 $60.49   13.526%   $68.6719   $68.67   $68.65   $68.70  
  Purchase #6 $239.83   11.453%   $267.2977   $267.30   $267.30   $267.30  
  Purchase #7 $236.30   13.143%   $267.3569   $267.36   $267.35   $267.40  
  7 purchase totals = $855.88       $960.4060   $960.41   $960.35   $960.60