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 $164.30   12.282%   $184.4793   $184.48   $184.50   $184.50  
  Purchase #2 $231.33   13.388%   $262.3005   $262.30   $262.30   $262.30  
  Purchase #3 $155.72   8.302%   $168.6479   $168.65   $168.65   $168.60  
  Purchase #4 $203.70   10.369%   $224.8217   $224.82   $224.80   $224.80  
  Purchase #5 $160.62   13.227%   $181.8652   $181.87   $181.85   $181.90  
  Purchase #6 $167.40   6.181%   $177.747   $177.75   $177.75   $177.70  
  Purchase #7 $151.96   9.509%   $166.4099   $166.41   $166.40   $166.40  
  7 purchase totals = $1,235.03       $1,366.2715   $1,366.28   $1,366.25   $1,366.20