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 $54.43   12.791%   $61.3921   $61.39   $61.40   $61.40  
  Purchase #2 $174.29   5.554%   $183.9701   $183.97   $183.95   $184.00  
  Purchase #3 $173.68   4.787%   $181.9941   $181.99   $182.00   $182.00  
  Purchase #4 $21.99   4.558%   $22.9923   $22.99   $23.00   $23.00  
  Purchase #5 $245.46   6.237%   $260.7693   $260.77   $260.75   $260.80  
  Purchase #6 $147.97   3.507%   $153.1593   $153.16   $153.15   $153.20  
  Purchase #7 $127.38   5.774%   $134.7349   $134.73   $134.75   $134.70  
  7 purchase totals = $945.20       $999.0121   $999.00   $999.00   $999.10