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 $186.73   3.282%   $192.8585   $192.86   $192.85   $192.90  
  Purchase #2 $34.99   8.627%   $38.0086   $38.01   $38.00   $38.00  
  Purchase #3 $46.60   11.620%   $52.0149   $52.01   $52.00   $52.00  
  Purchase #4 $203.78   6.832%   $217.7022   $217.70   $217.70   $217.70  
  Purchase #5 $63.99   13.722%   $72.7707   $72.77   $72.75   $72.80  
  Purchase #6 $240.65   10.282%   $265.3936   $265.39   $265.40   $265.40  
  Purchase #7 $161.49   8.348%   $174.9712   $174.97   $174.95   $175.00  
  7 purchase totals = $938.23       $1,013.7197   $1,013.71   $1,013.65   $1,013.80