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 $65.32   5.856%   $69.1451   $69.15   $69.15   $69.10  
  Purchase #2 $124.83   11.342%   $138.9882   $138.99   $139.00   $139.00  
  Purchase #3 $119.30   6.568%   $127.1356   $127.14   $127.15   $127.10  
  Purchase #4 $83.37   12.436%   $93.7379   $93.74   $93.75   $93.70  
  Purchase #5 $15.98   5.418%   $16.8458   $16.85   $16.85   $16.80  
  Purchase #6 $221.83   11.580%   $247.5179   $247.52   $247.50   $247.50  
  Purchase #7 $177.32   8.471%   $192.3408   $192.34   $192.35   $192.30  
  7 purchase totals = $807.95       $885.7113   $885.73   $885.75   $885.50