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 $86.66   7.232%   $92.9273   $92.93   $92.95   $92.90  
  Purchase #2 $96.88   7.464%   $104.1111   $104.11   $104.10   $104.10  
  Purchase #3 $135.82   3.604%   $140.715   $140.72   $140.70   $140.70  
  Purchase #4 $238.74   12.241%   $267.9642   $267.96   $267.95   $268.00  
  Purchase #5 $69.54   12.410%   $78.1699   $78.17   $78.15   $78.20  
  Purchase #6 $66.62   4.400%   $69.5513   $69.55   $69.55   $69.60  
  Purchase #7 $213.92   11.171%   $237.817   $237.82   $237.80   $237.80  
  7 purchase totals = $908.18       $991.2558   $991.26   $991.20   $991.30