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 $139.49   10.733%   $154.4615   $154.46   $154.45   $154.50  
  Purchase #2 $111.71   6.229%   $118.6684   $118.67   $118.65   $118.70  
  Purchase #3 $200.91   3.331%   $207.6023   $207.60   $207.60   $207.60  
  Purchase #4 $237.56   13.580%   $269.8206   $269.82   $269.80   $269.80  
  Purchase #5 $77.52   8.382%   $84.0177   $84.02   $84.00   $84.00  
  Purchase #6 $61.96   10.827%   $68.6684   $68.67   $68.65   $68.70  
  Purchase #7 $185.68   3.852%   $192.8324   $192.83   $192.85   $192.80  
  7 purchase totals = $1,014.83       $1,096.0713   $1,096.07   $1,096.00   $1,096.10