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 $46.37   8.266%   $50.2029   $50.20   $50.20   $50.20  
  Purchase #2 $220.75   4.621%   $230.9509   $230.95   $230.95   $231.00  
  Purchase #3 $73.41   3.593%   $76.0476   $76.05   $76.05   $76.00  
  Purchase #4 $93.70   10.639%   $103.6687   $103.67   $103.65   $103.70  
  Purchase #5 $189.61   3.258%   $195.7875   $195.79   $195.80   $195.80  
  Purchase #6 $237.80   10.384%   $262.4932   $262.49   $262.50   $262.50  
  Purchase #7 $134.86   7.262%   $144.6535   $144.65   $144.65   $144.70  
  7 purchase totals = $996.50       $1,063.8043   $1,063.80   $1,063.80   $1,063.90