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 $33.41   5.556%   $35.2663   $35.27   $35.25   $35.30  
  Purchase #2 $56.26   9.210%   $61.4415   $61.44   $61.45   $61.40  
  Purchase #3 $161.26   6.661%   $172.0015   $172.00   $172.00   $172.00  
  Purchase #4 $128.43   11.731%   $143.4961   $143.50   $143.50   $143.50  
  Purchase #5 $223.62   6.140%   $237.3503   $237.35   $237.35   $237.40  
  Purchase #6 $129.49   4.786%   $135.6874   $135.69   $135.70   $135.70  
  Purchase #7 $44.44   7.612%   $47.8228   $47.82   $47.80   $47.80  
  7 purchase totals = $776.91       $833.0659   $833.07   $833.05   $833.10