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 $212.53   5.858%   $224.98   $224.98   $225.00   $225.00  
  Purchase #2 $113.98   5.779%   $120.5669   $120.57   $120.55   $120.60  
  Purchase #3 $93.93   4.683%   $98.3287   $98.33   $98.35   $98.30  
  Purchase #4 $30.74   6.727%   $32.8079   $32.81   $32.80   $32.80  
  Purchase #5 $186.67   3.661%   $193.504   $193.50   $193.50   $193.50  
  Purchase #6 $15.80   6.220%   $16.7828   $16.78   $16.80   $16.80  
  Purchase #7 $150.52   12.274%   $168.9948   $168.99   $169.00   $169.00  
  7 purchase totals = $804.17       $855.9651   $855.96   $856.00   $856.00