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 $208.95   10.559%   $231.013   $231.01   $231.00   $231.00  
  Purchase #2 $184.44   10.615%   $204.0183   $204.02   $204.00   $204.00  
  Purchase #3 $100.98   8.602%   $109.6663   $109.67   $109.65   $109.70  
  Purchase #4 $227.57   8.152%   $246.1215   $246.12   $246.10   $246.10  
  Purchase #5 $39.43   7.143%   $42.2465   $42.25   $42.25   $42.20  
  Purchase #6 $136.75   7.312%   $146.7492   $146.75   $146.75   $146.70  
  Purchase #7 $75.41   4.531%   $78.8268   $78.83   $78.85   $78.80  
  7 purchase totals = $973.53       $1,058.6416   $1,058.65   $1,058.60   $1,058.50