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 $153.73   11.412%   $171.2737   $171.27   $171.25   $171.30  
  Purchase #2 $123.81   9.279%   $135.2983   $135.30   $135.30   $135.30  
  Purchase #3 $81.72   11.374%   $91.0148   $91.01   $91.00   $91.00  
  Purchase #4 $32.77   3.712%   $33.9864   $33.99   $34.00   $34.00  
  Purchase #5 $56.80   13.605%   $64.5276   $64.53   $64.55   $64.50  
  Purchase #6 $62.54   8.256%   $67.7033   $67.70   $67.70   $67.70  
  Purchase #7 $127.60   6.579%   $135.9948   $135.99   $136.00   $136.00  
  7 purchase totals = $638.97       $699.7989   $699.79   $699.80   $699.80