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 $201.69   11.319%   $224.5193   $224.52   $224.50   $224.50  
  Purchase #2 $51.38   4.386%   $53.6335   $53.63   $53.65   $53.60  
  Purchase #3 $188.45   5.424%   $198.6715   $198.67   $198.65   $198.70  
  Purchase #4 $55.80   11.192%   $62.0451   $62.05   $62.05   $62.00  
  Purchase #5 $66.80   13.818%   $76.0304   $76.03   $76.05   $76.00  
  Purchase #6 $181.50   7.519%   $195.147   $195.15   $195.15   $195.10  
  Purchase #7 $239.30   8.341%   $259.26   $259.26   $259.25   $259.30  
  7 purchase totals = $984.92       $1,069.3068   $1,069.31   $1,069.30   $1,069.20