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 $190.83   6.673%   $203.5641   $203.56   $203.55   $203.60  
  Purchase #2 $77.72   12.744%   $87.6246   $87.62   $87.60   $87.60  
  Purchase #3 $52.37   8.225%   $56.6774   $56.68   $56.70   $56.70  
  Purchase #4 $181.81   13.636%   $206.6016   $206.60   $206.60   $206.60  
  Purchase #5 $169.64   7.557%   $182.4597   $182.46   $182.45   $182.50  
  Purchase #6 $225.92   7.145%   $242.062   $242.06   $242.05   $242.10  
  Purchase #7 $82.76   13.824%   $94.2007   $94.20   $94.20   $94.20  
  7 purchase totals = $981.05       $1,073.1901   $1,073.18   $1,073.15   $1,073.30