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 $32.34   12.380%   $36.3437   $36.34   $36.35   $36.30  
  Purchase #2 $240.59   11.560%   $268.4022   $268.40   $268.40   $268.40  
  Purchase #3 $24.36   6.765%   $26.008   $26.01   $26.00   $26.00  
  Purchase #4 $84.33   13.367%   $95.6024   $95.60   $95.60   $95.60  
  Purchase #5 $233.98   9.414%   $256.0069   $256.01   $256.00   $256.00  
  Purchase #6 $47.50   3.464%   $49.1454   $49.15   $49.15   $49.10  
  Purchase #7 $138.72   12.283%   $155.759   $155.76   $155.75   $155.80  
  7 purchase totals = $801.82       $887.2676   $887.27   $887.25   $887.20