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 $68.37   8.723%   $74.3339   $74.33   $74.35   $74.30  
  Purchase #2 $218.58   7.741%   $235.5003   $235.50   $235.50   $235.50  
  Purchase #3 $18.81   8.223%   $20.3567   $20.36   $20.35   $20.40  
  Purchase #4 $234.48   10.193%   $258.3805   $258.38   $258.40   $258.40  
  Purchase #5 $232.81   7.791%   $250.9482   $250.95   $250.95   $250.90  
  Purchase #6 $47.82   6.180%   $50.7753   $50.78   $50.80   $50.80  
  Purchase #7 $115.69   11.231%   $128.6831   $128.68   $128.70   $128.70  
  7 purchase totals = $936.56       $1,018.9780   $1,018.98   $1,019.05   $1,019.00