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 $99.94   5.823%   $105.7595   $105.76   $105.75   $105.80  
  Purchase #2 $70.96   7.139%   $76.0258   $76.03   $76.05   $76.00  
  Purchase #3 $46.92   11.814%   $52.4631   $52.46   $52.45   $52.50  
  Purchase #4 $186.36   4.496%   $194.7387   $194.74   $194.75   $194.70  
  Purchase #5 $158.58   10.184%   $174.7298   $174.73   $174.75   $174.70  
  Purchase #6 $201.61   6.595%   $214.9062   $214.91   $214.90   $214.90  
  Purchase #7 $97.51   9.308%   $106.5862   $106.59   $106.60   $106.60  
  7 purchase totals = $861.88       $925.2093   $925.22   $925.25   $925.20