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 $65.70   8.555%   $71.3206   $71.32   $71.30   $71.30  
  Purchase #2 $132.81   9.604%   $145.5651   $145.57   $145.55   $145.60  
  Purchase #3 $228.97   13.739%   $260.4282   $260.43   $260.45   $260.40  
  Purchase #4 $157.89   12.267%   $177.2584   $177.26   $177.25   $177.30  
  Purchase #5 $49.95   13.295%   $56.5909   $56.59   $56.60   $56.60  
  Purchase #6 $42.93   12.169%   $48.1542   $48.15   $48.15   $48.20  
  Purchase #7 $234.85   8.242%   $254.2063   $254.21   $254.20   $254.20  
  7 purchase totals = $913.10       $1,013.5237   $1,013.53   $1,013.50   $1,013.60