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 $149.91   12.717%   $168.9741   $168.97   $168.95   $169.00  
  Purchase #2 $219.93   6.401%   $234.0077   $234.01   $234.00   $234.00  
  Purchase #3 $38.40   13.284%   $43.5011   $43.50   $43.50   $43.50  
  Purchase #4 $172.62   10.678%   $191.0524   $191.05   $191.05   $191.10  
  Purchase #5 $93.51   6.469%   $99.5592   $99.56   $99.55   $99.60  
  Purchase #6 $188.79   10.151%   $207.9541   $207.95   $207.95   $208.00  
  Purchase #7 $233.32   13.556%   $264.9489   $264.95   $264.95   $264.90  
  7 purchase totals = $1,096.48       $1,209.9975   $1,209.99   $1,209.95   $1,210.10