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 $89.94   3.509%   $93.096   $93.10   $93.10   $93.10  
  Purchase #2 $143.25   3.242%   $147.8942   $147.89   $147.90   $147.90  
  Purchase #3 $216.37   9.242%   $236.3669   $236.37   $236.35   $236.40  
  Purchase #4 $205.47   10.106%   $226.2348   $226.23   $226.25   $226.20  
  Purchase #5 $152.99   8.198%   $165.5321   $165.53   $165.55   $165.50  
  Purchase #6 $168.25   9.441%   $184.1345   $184.13   $184.15   $184.10  
  Purchase #7 $46.88   7.867%   $50.568   $50.57   $50.55   $50.60  
  7 purchase totals = $1,023.15       $1,103.8265   $1,103.82   $1,103.85   $1,103.80