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 $119.76   8.559%   $130.0103   $130.01   $130.00   $130.00  
  Purchase #2 $55.65   10.655%   $61.5795   $61.58   $61.60   $61.60  
  Purchase #3 $177.90   8.323%   $192.7066   $192.71   $192.70   $192.70  
  Purchase #4 $233.69   6.127%   $248.0082   $248.01   $248.00   $248.00  
  Purchase #5 $106.95   13.552%   $121.4439   $121.44   $121.45   $121.40  
  Purchase #6 $145.84   4.800%   $152.8403   $152.84   $152.85   $152.80  
  Purchase #7 $138.70   5.197%   $145.9082   $145.91   $145.90   $145.90  
  7 purchase totals = $978.49       $1,052.4970   $1,052.50   $1,052.50   $1,052.40