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 $202.89   10.422%   $224.0352   $224.04   $224.05   $224.00  
  Purchase #2 $74.83   4.302%   $78.0492   $78.05   $78.05   $78.00  
  Purchase #3 $105.38   4.693%   $110.3255   $110.33   $110.35   $110.30  
  Purchase #4 $241.69   4.488%   $252.537   $252.54   $252.55   $252.50  
  Purchase #5 $30.25   10.330%   $33.3748   $33.37   $33.35   $33.40  
  Purchase #6 $48.63   11.506%   $54.2254   $54.23   $54.25   $54.20  
  Purchase #7 $52.82   10.796%   $58.5224   $58.52   $58.50   $58.50  
  7 purchase totals = $756.49       $811.0695   $811.08   $811.10   $810.90