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 $148.42   3.509%   $153.6281   $153.63   $153.65   $153.60  
  Purchase #2 $42.79   12.762%   $48.2509   $48.25   $48.25   $48.30  
  Purchase #3 $91.65   8.699%   $99.6226   $99.62   $99.60   $99.60  
  Purchase #4 $141.68   5.341%   $149.2471   $149.25   $149.25   $149.20  
  Purchase #5 $55.99   5.737%   $59.2021   $59.20   $59.20   $59.20  
  Purchase #6 $237.74   13.204%   $269.1312   $269.13   $269.15   $269.10  
  Purchase #7 $160.39   6.783%   $171.2693   $171.27   $171.25   $171.30  
  7 purchase totals = $878.66       $950.3513   $950.35   $950.35   $950.30