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 $167.94   4.802%   $176.0045   $176.00   $176.00   $176.00  
  Purchase #2 $120.66   3.310%   $124.6538   $124.65   $124.65   $124.70  
  Purchase #3 $89.93   8.255%   $97.3537   $97.35   $97.35   $97.40  
  Purchase #4 $26.85   3.714%   $27.8472   $27.85   $27.85   $27.80  
  Purchase #5 $219.93   13.247%   $249.0641   $249.06   $249.05   $249.10  
  Purchase #6 $31.85   10.797%   $35.2888   $35.29   $35.30   $35.30  
  Purchase #7 $185.39   6.552%   $197.5368   $197.54   $197.55   $197.50  
  7 purchase totals = $842.55       $907.7489   $907.74   $907.75   $907.80