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 $219.81   4.536%   $229.7806   $229.78   $229.80   $229.80  
  Purchase #2 $212.67   12.363%   $238.9624   $238.96   $238.95   $239.00  
  Purchase #3 $76.37   11.187%   $84.9135   $84.91   $84.90   $84.90  
  Purchase #4 $202.96   10.359%   $223.9846   $223.98   $224.00   $224.00  
  Purchase #5 $136.52   6.681%   $145.6409   $145.64   $145.65   $145.60  
  Purchase #6 $60.76   5.779%   $64.2713   $64.27   $64.25   $64.30  
  Purchase #7 $44.48   8.845%   $48.4143   $48.41   $48.40   $48.40  
  7 purchase totals = $953.57       $1,035.9676   $1,035.95   $1,035.95   $1,036.00