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 $68.25   12.644%   $76.8795   $76.88   $76.90   $76.90  
  Purchase #2 $68.52   8.477%   $74.3284   $74.33   $74.35   $74.30  
  Purchase #3 $93.65   6.486%   $99.7241   $99.72   $99.70   $99.70  
  Purchase #4 $106.66   8.457%   $115.6802   $115.68   $115.70   $115.70  
  Purchase #5 $51.56   8.369%   $55.8751   $55.88   $55.90   $55.90  
  Purchase #6 $250.40   5.483%   $264.1294   $264.13   $264.15   $264.10  
  Purchase #7 $147.44   7.596%   $158.6395   $158.64   $158.65   $158.60  
  7 purchase totals = $786.48       $845.2562   $845.26   $845.35   $845.20