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 $58.61   4.411%   $61.1953   $61.20   $61.20   $61.20  
  Purchase #2 $229.58   4.303%   $239.4588   $239.46   $239.45   $239.50  
  Purchase #3 $182.61   8.750%   $198.5884   $198.59   $198.60   $198.60  
  Purchase #4 $71.75   6.718%   $76.5702   $76.57   $76.55   $76.60  
  Purchase #5 $94.66   3.487%   $97.9608   $97.96   $97.95   $98.00  
  Purchase #6 $80.41   13.814%   $91.5178   $91.52   $91.50   $91.50  
  Purchase #7 $37.99   4.631%   $39.7493   $39.75   $39.75   $39.70  
  7 purchase totals = $755.61       $805.0406   $805.05   $805.00   $805.10