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 $162.77   3.565%   $168.5728   $168.57   $168.55   $168.60  
  Purchase #2 $187.29   13.306%   $212.2108   $212.21   $212.20   $212.20  
  Purchase #3 $241.69   8.778%   $262.9055   $262.91   $262.90   $262.90  
  Purchase #4 $176.52   8.807%   $192.0661   $192.07   $192.05   $192.10  
  Purchase #5 $153.65   13.306%   $174.0947   $174.09   $174.10   $174.10  
  Purchase #6 $5.28   6.439%   $5.62   $5.62   $5.60   $5.60  
  Purchase #7 $198.79   9.650%   $217.9732   $217.97   $217.95   $218.00  
  7 purchase totals = $1,125.99       $1,233.4431   $1,233.44   $1,233.35   $1,233.50