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 $30.68   7.708%   $33.0448   $33.04   $33.05   $33.00  
  Purchase #2 $205.34   11.190%   $228.3175   $228.32   $228.30   $228.30  
  Purchase #3 $80.52   4.200%   $83.9018   $83.90   $83.90   $83.90  
  Purchase #4 $216.76   6.682%   $231.2439   $231.24   $231.25   $231.20  
  Purchase #5 $98.28   11.328%   $109.4132   $109.41   $109.40   $109.40  
  Purchase #6 $156.80   6.375%   $166.796   $166.80   $166.80   $166.80  
  Purchase #7 $193.99   6.509%   $206.6168   $206.62   $206.60   $206.60  
  7 purchase totals = $982.37       $1,059.3340   $1,059.33   $1,059.30   $1,059.20