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 $56.73   9.159%   $61.9259   $61.93   $61.95   $61.90  
  Purchase #2 $200.35   12.502%   $225.3978   $225.40   $225.40   $225.40  
  Purchase #3 $78.72   11.245%   $87.5721   $87.57   $87.55   $87.60  
  Purchase #4 $71.59   8.577%   $77.7303   $77.73   $77.75   $77.70  
  Purchase #5 $160.69   9.743%   $176.346   $176.35   $176.35   $176.30  
  Purchase #6 $161.90   3.131%   $166.9691   $166.97   $166.95   $167.00  
  Purchase #7 $49.50   6.846%   $52.8888   $52.89   $52.90   $52.90  
  7 purchase totals = $779.48       $848.8300   $848.84   $848.85   $848.80