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 $46.28   3.793%   $48.0354   $48.04   $48.05   $48.00  
  Purchase #2 $168.57   6.617%   $179.7243   $179.72   $179.70   $179.70  
  Purchase #3 $138.28   13.838%   $157.4152   $157.42   $157.40   $157.40  
  Purchase #4 $226.35   4.219%   $235.8997   $235.90   $235.90   $235.90  
  Purchase #5 $117.31   10.409%   $129.5208   $129.52   $129.50   $129.50  
  Purchase #6 $55.81   9.651%   $61.1962   $61.20   $61.20   $61.20  
  Purchase #7 $203.53   5.173%   $214.0586   $214.06   $214.05   $214.10  
  7 purchase totals = $956.13       $1,025.8502   $1,025.86   $1,025.80   $1,025.80