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 $55.25   11.666%   $61.6955   $61.70   $61.70   $61.70  
  Purchase #2 $135.37   12.804%   $152.7028   $152.70   $152.70   $152.70  
  Purchase #3 $156.82   12.546%   $176.4946   $176.49   $176.50   $176.50  
  Purchase #4 $228.86   6.544%   $243.8366   $243.84   $243.85   $243.80  
  Purchase #5 $59.98   6.239%   $63.7222   $63.72   $63.70   $63.70  
  Purchase #6 $192.63   4.815%   $201.9051   $201.91   $201.90   $201.90  
  Purchase #7 $78.91   13.611%   $89.6504   $89.65   $89.65   $89.70  
  7 purchase totals = $907.82       $990.0072   $990.01   $990.00   $990.00