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 $43.59   9.597%   $47.7733   $47.77   $47.75   $47.80  
  Purchase #2 $174.47   6.480%   $185.7757   $185.78   $185.80   $185.80  
  Purchase #3 $201.41   5.736%   $212.9629   $212.96   $212.95   $213.00  
  Purchase #4 $177.54   8.537%   $192.6966   $192.70   $192.70   $192.70  
  Purchase #5 $167.76   13.874%   $191.035   $191.04   $191.05   $191.00  
  Purchase #6 $193.88   9.368%   $212.0427   $212.04   $212.05   $212.00  
  Purchase #7 $237.77   9.550%   $260.477   $260.48   $260.50   $260.50  
  7 purchase totals = $1,196.42       $1,302.7632   $1,302.77   $1,302.80   $1,302.80