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 $154.52   5.652%   $163.2535   $163.25   $163.25   $163.30  
  Purchase #2 $209.33   10.327%   $230.9475   $230.95   $230.95   $230.90  
  Purchase #3 $46.31   12.791%   $52.2335   $52.23   $52.25   $52.20  
  Purchase #4 $138.38   10.770%   $153.2835   $153.28   $153.30   $153.30  
  Purchase #5 $162.73   3.804%   $168.9202   $168.92   $168.90   $168.90  
  Purchase #6 $127.85   12.118%   $143.3429   $143.34   $143.35   $143.30  
  Purchase #7 $145.64   3.426%   $150.6296   $150.63   $150.65   $150.60  
  7 purchase totals = $984.76       $1,062.6107   $1,062.60   $1,062.65   $1,062.50