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 $206.74   8.629%   $224.5796   $224.58   $224.60   $224.60  
  Purchase #2 $50.65   8.315%   $54.8615   $54.86   $54.85   $54.90  
  Purchase #3 $232.49   8.348%   $251.8983   $251.90   $251.90   $251.90  
  Purchase #4 $220.94   5.635%   $233.39   $233.39   $233.40   $233.40  
  Purchase #5 $170.84   6.598%   $182.112   $182.11   $182.10   $182.10  
  Purchase #6 $54.64   7.165%   $58.555   $58.56   $58.55   $58.60  
  Purchase #7 $158.75   12.383%   $178.408   $178.41   $178.40   $178.40  
  7 purchase totals = $1,095.05       $1,183.8044   $1,183.81   $1,183.80   $1,183.90