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 $211.90   3.596%   $219.5199   $219.52   $219.50   $219.50  
  Purchase #2 $233.41   13.685%   $265.3522   $265.35   $265.35   $265.40  
  Purchase #3 $226.91   12.659%   $255.6345   $255.63   $255.65   $255.60  
  Purchase #4 $238.34   3.581%   $246.875   $246.88   $246.90   $246.90  
  Purchase #5 $13.57   13.235%   $15.366   $15.37   $15.35   $15.40  
  Purchase #6 $95.81   8.359%   $103.8188   $103.82   $103.80   $103.80  
  Purchase #7 $228.45   8.326%   $247.4707   $247.47   $247.45   $247.50  
  7 purchase totals = $1,248.39       $1,354.0371   $1,354.04   $1,354.00   $1,354.10