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 $159.55   11.502%   $177.9014   $177.90   $177.90   $177.90  
  Purchase #2 $57.38   7.397%   $61.6244   $61.62   $61.60   $61.60  
  Purchase #3 $151.72   8.549%   $164.6905   $164.69   $164.70   $164.70  
  Purchase #4 $165.53   13.158%   $187.3104   $187.31   $187.30   $187.30  
  Purchase #5 $141.65   13.122%   $160.2373   $160.24   $160.25   $160.20  
  Purchase #6 $197.46   11.653%   $220.47   $220.47   $220.45   $220.50  
  Purchase #7 $35.65   6.791%   $38.071   $38.07   $38.05   $38.10  
  7 purchase totals = $908.94       $1,010.3050   $1,010.30   $1,010.25   $1,010.30