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 $135.73   13.603%   $154.1934   $154.19   $154.20   $154.20  
  Purchase #2 $160.32   5.778%   $169.5833   $169.58   $169.60   $169.60  
  Purchase #3 $159.28   11.166%   $177.0652   $177.07   $177.05   $177.10  
  Purchase #4 $53.61   3.529%   $55.5019   $55.50   $55.50   $55.50  
  Purchase #5 $228.40   10.765%   $252.9873   $252.99   $253.00   $253.00  
  Purchase #6 $48.30   3.473%   $49.9775   $49.98   $50.00   $50.00  
  Purchase #7 $151.91   6.838%   $162.2976   $162.30   $162.30   $162.30  
  7 purchase totals = $937.55       $1,021.6062   $1,021.61   $1,021.65   $1,021.70