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 $188.44   8.271%   $204.0259   $204.03   $204.05   $204.00  
  Purchase #2 $136.32   12.242%   $153.0083   $153.01   $153.00   $153.00  
  Purchase #3 $36.92   10.287%   $40.718   $40.72   $40.70   $40.70  
  Purchase #4 $112.31   5.871%   $118.9037   $118.90   $118.90   $118.90  
  Purchase #5 $56.31   5.819%   $59.5867   $59.59   $59.60   $59.60  
  Purchase #6 $47.81   4.173%   $49.8051   $49.81   $49.80   $49.80  
  Purchase #7 $237.65   9.159%   $259.4164   $259.42   $259.40   $259.40  
  7 purchase totals = $815.76       $885.4641   $885.48   $885.45   $885.40