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 $174.53   13.417%   $197.9467   $197.95   $197.95   $197.90  
  Purchase #2 $173.77   11.572%   $193.8787   $193.88   $193.90   $193.90  
  Purchase #3 $220.77   5.387%   $232.6629   $232.66   $232.65   $232.70  
  Purchase #4 $117.56   9.844%   $129.1326   $129.13   $129.15   $129.10  
  Purchase #5 $72.29   12.731%   $81.4932   $81.49   $81.50   $81.50  
  Purchase #6 $88.50   4.699%   $92.6586   $92.66   $92.65   $92.70  
  Purchase #7 $103.25   5.188%   $108.6066   $108.61   $108.60   $108.60  
  7 purchase totals = $950.67       $1,036.3793   $1,036.38   $1,036.40   $1,036.40