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 $194.87   11.584%   $217.4437   $217.44   $217.45   $217.40  
  Purchase #2 $139.74   10.514%   $154.4323   $154.43   $154.45   $154.40  
  Purchase #3 $47.65   10.572%   $52.6876   $52.69   $52.70   $52.70  
  Purchase #4 $236.75   9.762%   $259.8615   $259.86   $259.85   $259.90  
  Purchase #5 $13.39   10.269%   $14.765   $14.77   $14.75   $14.80  
  Purchase #6 $120.92   8.582%   $131.2974   $131.30   $131.30   $131.30  
  Purchase #7 $172.65   11.696%   $192.8431   $192.84   $192.85   $192.80  
  7 purchase totals = $925.97       $1,023.3306   $1,023.33   $1,023.35   $1,023.30