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 $55.45   13.306%   $62.8282   $62.83   $62.85   $62.80  
  Purchase #2 $131.40   4.264%   $137.0029   $137.00   $137.00   $137.00  
  Purchase #3 $68.90   11.813%   $77.0392   $77.04   $77.05   $77.00  
  Purchase #4 $229.37   6.114%   $243.3937   $243.39   $243.40   $243.40  
  Purchase #5 $198.36   9.150%   $216.5099   $216.51   $216.50   $216.50  
  Purchase #6 $44.41   7.682%   $47.8216   $47.82   $47.80   $47.80  
  Purchase #7 $128.62   13.273%   $145.6917   $145.69   $145.70   $145.70  
  7 purchase totals = $856.51       $930.2872   $930.28   $930.30   $930.20