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 $111.44   7.311%   $119.5874   $119.59   $119.60   $119.60  
  Purchase #2 $245.76   8.867%   $267.5515   $267.55   $267.55   $267.60  
  Purchase #3 $100.95   11.272%   $112.3291   $112.33   $112.35   $112.30  
  Purchase #4 $205.98   7.769%   $221.9826   $221.98   $222.00   $222.00  
  Purchase #5 $75.68   6.602%   $80.6764   $80.68   $80.70   $80.70  
  Purchase #6 $57.99   11.470%   $64.6415   $64.64   $64.65   $64.60  
  Purchase #7 $174.27   10.614%   $192.767   $192.77   $192.75   $192.80  
  7 purchase totals = $972.07       $1,059.5355   $1,059.54   $1,059.60   $1,059.60