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 $156.27   10.418%   $172.5502   $172.55   $172.55   $172.60  
  Purchase #2 $34.99   10.675%   $38.7252   $38.73   $38.75   $38.70  
  Purchase #3 $142.79   10.331%   $157.5416   $157.54   $157.55   $157.50  
  Purchase #4 $103.89   5.801%   $109.9167   $109.92   $109.90   $109.90  
  Purchase #5 $53.48   4.642%   $55.9625   $55.96   $55.95   $56.00  
  Purchase #6 $150.88   6.295%   $160.3779   $160.38   $160.40   $160.40  
  Purchase #7 $171.45   3.699%   $177.7919   $177.79   $177.80   $177.80  
  7 purchase totals = $813.75       $872.8660   $872.87   $872.90   $872.90