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 $183.87   5.272%   $193.5636   $193.56   $193.55   $193.60  
  Purchase #2 $15.87   5.804%   $16.7911   $16.79   $16.80   $16.80  
  Purchase #3 $186.60   10.838%   $206.8237   $206.82   $206.80   $206.80  
  Purchase #4 $85.37   11.415%   $95.115   $95.12   $95.10   $95.10  
  Purchase #5 $76.43   13.429%   $86.6938   $86.69   $86.70   $86.70  
  Purchase #6 $149.88   10.484%   $165.5934   $165.59   $165.60   $165.60  
  Purchase #7 $84.77   9.172%   $92.5451   $92.55   $92.55   $92.50  
  7 purchase totals = $782.79       $857.1257   $857.12   $857.10   $857.10