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 $32.66   4.276%   $34.0565   $34.06   $34.05   $34.10  
  Purchase #2 $176.38   11.693%   $197.0041   $197.00   $197.00   $197.00  
  Purchase #3 $243.81   3.211%   $251.6387   $251.64   $251.65   $251.60  
  Purchase #4 $178.78   9.692%   $196.1074   $196.11   $196.10   $196.10  
  Purchase #5 $10.56   3.514%   $10.9311   $10.93   $10.95   $10.90  
  Purchase #6 $43.38   11.849%   $48.5201   $48.52   $48.50   $48.50  
  Purchase #7 $32.69   13.452%   $37.0875   $37.09   $37.10   $37.10  
  7 purchase totals = $718.26       $775.3454   $775.35   $775.35   $775.30