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 $212.56   11.852%   $237.7526   $237.75   $237.75   $237.80  
  Purchase #2 $160.47   10.526%   $177.3611   $177.36   $177.35   $177.40  
  Purchase #3 $51.51   13.183%   $58.3006   $58.30   $58.30   $58.30  
  Purchase #4 $15.26   8.582%   $16.5696   $16.57   $16.55   $16.60  
  Purchase #5 $189.55   5.473%   $199.9241   $199.92   $199.90   $199.90  
  Purchase #6 $151.68   8.606%   $164.7336   $164.73   $164.75   $164.70  
  Purchase #7 $184.54   10.308%   $203.5624   $203.56   $203.55   $203.60  
  7 purchase totals = $965.57       $1,058.2040   $1,058.19   $1,058.15   $1,058.30