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 $215.81   10.654%   $238.8024   $238.80   $238.80   $238.80  
  Purchase #2 $247.55   13.490%   $280.9445   $280.94   $280.95   $280.90  
  Purchase #3 $166.34   5.509%   $175.5037   $175.50   $175.50   $175.50  
  Purchase #4 $29.87   8.685%   $32.4642   $32.46   $32.45   $32.50  
  Purchase #5 $80.98   10.160%   $89.2076   $89.21   $89.20   $89.20  
  Purchase #6 $149.67   3.242%   $154.5223   $154.52   $154.50   $154.50  
  Purchase #7 $220.99   6.502%   $235.3588   $235.36   $235.35   $235.40  
  7 purchase totals = $1,111.21       $1,206.8035   $1,206.79   $1,206.75   $1,206.80