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 $129.97   11.293%   $144.6475   $144.65   $144.65   $144.60  
  Purchase #2 $16.98   6.110%   $18.0175   $18.02   $18.00   $18.00  
  Purchase #3 $82.72   12.653%   $93.1866   $93.19   $93.20   $93.20  
  Purchase #4 $231.52   6.359%   $246.2424   $246.24   $246.25   $246.20  
  Purchase #5 $158.41   8.116%   $171.2666   $171.27   $171.25   $171.30  
  Purchase #6 $60.79   3.607%   $62.9827   $62.98   $63.00   $63.00  
  Purchase #7 $41.84   13.264%   $47.3897   $47.39   $47.40   $47.40  
  7 purchase totals = $722.23       $783.7330   $783.74   $783.75   $783.70