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 $174.75   6.762%   $186.5666   $186.57   $186.55   $186.60  
  Purchase #2 $232.68   13.179%   $263.3449   $263.34   $263.35   $263.30  
  Purchase #3 $72.58   11.799%   $81.1437   $81.14   $81.15   $81.10  
  Purchase #4 $11.45   7.659%   $12.327   $12.33   $12.35   $12.30  
  Purchase #5 $115.30   7.593%   $124.0547   $124.05   $124.05   $124.10  
  Purchase #6 $33.92   8.241%   $36.7153   $36.72   $36.70   $36.70  
  Purchase #7 $186.66   8.811%   $203.1066   $203.11   $203.10   $203.10  
  7 purchase totals = $827.34       $907.2588   $907.26   $907.25   $907.20