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 $206.74   3.614%   $214.2116   $214.21   $214.20   $214.20  
  Purchase #2 $166.83   5.690%   $176.3226   $176.32   $176.30   $176.30  
  Purchase #3 $181.73   10.826%   $201.4041   $201.40   $201.40   $201.40  
  Purchase #4 $31.29   13.510%   $35.5173   $35.52   $35.50   $35.50  
  Purchase #5 $151.38   9.120%   $165.1859   $165.19   $165.20   $165.20  
  Purchase #6 $62.92   11.197%   $69.9652   $69.97   $69.95   $70.00  
  Purchase #7 $190.68   12.333%   $214.1966   $214.20   $214.20   $214.20  
  7 purchase totals = $991.57       $1,076.8033   $1,076.81   $1,076.75   $1,076.80