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 $192.43   5.511%   $203.0348   $203.03   $203.05   $203.00  
  Purchase #2 $218.30   7.318%   $234.2752   $234.28   $234.30   $234.30  
  Purchase #3 $59.77   9.860%   $65.6633   $65.66   $65.65   $65.70  
  Purchase #4 $69.79   13.234%   $79.026   $79.03   $79.05   $79.00  
  Purchase #5 $184.56   11.671%   $206.1   $206.10   $206.10   $206.10  
  Purchase #6 $165.76   5.838%   $175.4371   $175.44   $175.45   $175.40  
  Purchase #7 $59.52   10.553%   $65.8011   $65.80   $65.80   $65.80  
  7 purchase totals = $950.13       $1,029.3375   $1,029.34   $1,029.40   $1,029.30