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 $129.28   4.800%   $135.4854   $135.49   $135.50   $135.50  
  Purchase #2 $203.83   8.720%   $221.604   $221.60   $221.60   $221.60  
  Purchase #3 $139.72   11.711%   $156.0826   $156.08   $156.10   $156.10  
  Purchase #4 $119.67   9.553%   $131.1021   $131.10   $131.10   $131.10  
  Purchase #5 $174.57   4.714%   $182.7992   $182.80   $182.80   $182.80  
  Purchase #6 $78.41   6.106%   $83.1977   $83.20   $83.20   $83.20  
  Purchase #7 $163.52   10.746%   $181.0919   $181.09   $181.10   $181.10  
  7 purchase totals = $1,009.00       $1,091.3629   $1,091.36   $1,091.40   $1,091.40