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 $61.61   13.353%   $69.8368   $69.84   $69.85   $69.80  
  Purchase #2 $169.77   11.766%   $189.7451   $189.75   $189.75   $189.70  
  Purchase #3 $166.72   6.448%   $177.4701   $177.47   $177.45   $177.50  
  Purchase #4 $162.59   5.328%   $171.2528   $171.25   $171.25   $171.30  
  Purchase #5 $109.85   11.454%   $122.4322   $122.43   $122.45   $122.40  
  Purchase #6 $157.95   7.291%   $169.4661   $169.47   $169.45   $169.50  
  Purchase #7 $180.29   11.538%   $201.0919   $201.09   $201.10   $201.10  
  7 purchase totals = $1,008.78       $1,101.2950   $1,101.30   $1,101.30   $1,101.30