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 $203.44   5.153%   $213.9233   $213.92   $213.90   $213.90  
  Purchase #2 $212.38   8.575%   $230.5916   $230.59   $230.60   $230.60  
  Purchase #3 $31.72   6.517%   $33.7872   $33.79   $33.80   $33.80  
  Purchase #4 $221.43   9.533%   $242.5389   $242.54   $242.55   $242.50  
  Purchase #5 $230.25   6.455%   $245.1126   $245.11   $245.10   $245.10  
  Purchase #6 $39.51   5.274%   $41.5938   $41.59   $41.60   $41.60  
  Purchase #7 $51.99   6.509%   $55.374   $55.37   $55.35   $55.40  
  7 purchase totals = $990.72       $1,062.9214   $1,062.91   $1,062.90   $1,062.90