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 $84.52   12.714%   $95.2659   $95.27   $95.25   $95.30  
  Purchase #2 $219.52   8.649%   $238.5063   $238.51   $238.50   $238.50  
  Purchase #3 $198.61   4.339%   $207.2277   $207.23   $207.25   $207.20  
  Purchase #4 $41.71   4.248%   $43.4818   $43.48   $43.50   $43.50  
  Purchase #5 $70.76   13.802%   $80.5263   $80.53   $80.55   $80.50  
  Purchase #6 $72.50   4.447%   $75.7241   $75.72   $75.70   $75.70  
  Purchase #7 $57.79   9.352%   $63.1945   $63.19   $63.20   $63.20  
  7 purchase totals = $745.41       $803.9266   $803.93   $803.95   $803.90