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 $67.58   9.289%   $73.8575   $73.86   $73.85   $73.90  
  Purchase #2 $20.82   12.236%   $23.3675   $23.37   $23.35   $23.40  
  Purchase #3 $240.65   13.727%   $273.684   $273.68   $273.70   $273.70  
  Purchase #4 $122.49   8.815%   $133.2875   $133.29   $133.30   $133.30  
  Purchase #5 $173.43   7.778%   $186.9194   $186.92   $186.90   $186.90  
  Purchase #6 $39.59   7.572%   $42.5878   $42.59   $42.60   $42.60  
  Purchase #7 $198.32   11.464%   $221.0554   $221.06   $221.05   $221.10  
  7 purchase totals = $862.88       $954.7591   $954.77   $954.75   $954.90