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 $165.71   10.422%   $182.9803   $182.98   $183.00   $183.00  
  Purchase #2 $150.97   13.658%   $171.5895   $171.59   $171.60   $171.60  
  Purchase #3 $172.80   11.375%   $192.456   $192.46   $192.45   $192.50  
  Purchase #4 $108.95   5.532%   $114.9771   $114.98   $115.00   $115.00  
  Purchase #5 $26.78   7.405%   $28.7631   $28.76   $28.75   $28.80  
  Purchase #6 $232.71   4.435%   $243.0307   $243.03   $243.05   $243.00  
  Purchase #7 $35.59   6.716%   $37.9802   $37.98   $38.00   $38.00  
  7 purchase totals = $893.51       $971.7769   $971.78   $971.85   $971.90