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 $135.64   7.383%   $145.6543   $145.65   $145.65   $145.70  
  Purchase #2 $87.68   9.211%   $95.7562   $95.76   $95.75   $95.80  
  Purchase #3 $156.29   9.104%   $170.5186   $170.52   $170.50   $170.50  
  Purchase #4 $53.78   4.580%   $56.2431   $56.24   $56.25   $56.20  
  Purchase #5 $161.32   5.799%   $170.6749   $170.67   $170.65   $170.70  
  Purchase #6 $182.47   4.466%   $190.6191   $190.62   $190.60   $190.60  
  Purchase #7 $122.58   11.396%   $136.5492   $136.55   $136.55   $136.50  
  7 purchase totals = $899.76       $966.0154   $966.01   $965.95   $966.00